Re: learning Python
On 28/10/24 11:51, o1bigtenor via Python-list wrote: Greetings There are mountains of books out there. Any suggestions for documents for a just learning how to program and starting with Python (3)? Preference to a tool where I would be learning by doing - - - that works well for me. Coursera and edX have many courses. Harvard CS50-P (for Python) may suit... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Python 3.8 or later on Debian?
On 19/09/24 02:49, Ulrich Goebel via Python-list wrote: Hi, Debian Linux seems to love Python 3.7 - that is shown by apt-get list, and it's installed on my Debian Server. But I need at least Python 3.8 Is there a repository which I can give to apt to get Python 3.8 or later? Or do I really have to install and compile these versions manually? I'm not a friend of things so deep in the system... Assumptions: 1 "need" for a particular project, cf system-wide 2 use of a virtual-environment for project(s) Try pyenv (https://github.com/pyenv/pyenv). It offers a list of Python versions. When downloaded, it builds a version for you - assuming have build-environment s/w in place. (this is where my lack of Debian knowledge may become obvious) Thereafter, within the project's virtual-environment can select which (installed-version of) Python is to be used. Am sure there are plenty of how-to-installs. Here's one: https://bgasparotto.com/install-pyenv-ubuntu-debian Am using pyenv to support multiple projects initially built during the reign of multiple Python versions (which now update annually - next is about two weeks away). -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Crash when launching python
On 5/09/24 03:27, Guenther Sohler via Python-list wrote: Hi, My "Project" is to integrate python support into OpenSCAD. It runs quite well, but there are still issues on MacOS. On My MacOS it works, but it crashes when I ship the DMG files. It looks very much like python is not able to find the "startup" python files and therefore crashes. Is it possible to turn on debugging and to display on the console, where python is loading files from ? (am not a Mac user) Starting with 'the basics', are you familiar with: 5. Using Python on a Mac https://docs.python.org/3/using/mac.html (and the more general preceding sections) This doc likely includes mention of such parameters: 1.2. Environment variables https://docs.python.org/3/using/cmdline.html#environment-variables Here is a library for programmatic manipulation: site — Site-specific configuration hook https://docs.python.org/3/library/site.html#module-site Please let us know how things progress... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Formatting a str as a number - Okay, one more related thing...
On 1/09/24 06:55, MRAB via Python-list wrote:
On 2024-08-31 06:31, Gilmeh Serda via Python-list wrote:
On Fri, 30 Aug 2024 05:22:17 GMT, Gilmeh Serda wrote:
f"{int(number):>20,}"
I can find "," (comma) and I can find "_" (underscore) but how about " "
(space)?
Or any other character, for that matter?
Any ideas?
Of course I can do f"{123456:>20_}".replace("_", " "), just thought there
might be something else my search mojo fails on.
The format is described here:
https://docs.python.org/3/library/string.html#formatspec
A space is counted as a fill character.
Rather than strict formatting, you may be venturing into
"internationalisation/localisation" thinking.
Different cultures/languages present numeric-amounts in their own ways.
For example, a decimal point may look like a dot or period to some
(there's two words for the same symbol from different English-language
cultures!), whereas in Europe the symbol others call a comma is used, eg
123.45 or 123,45 - and that's just one complication of convention...
For your reading pleasure, please review "locales"
(https://docs.python.org/3/library/locale.html)
Here's an example:
Country Integer Float
USA 123,456 123,456.78
France 123 456 123 456,78
Spain 123.456 123.456,78
Portugal 123456 123456,78
Poland 123 456 123 456,78
Here's some old code, filched from somewhere (above web.ref?) and
updated today to produce the above:-
""" PythonExperiments:locale_numbers.py
Demonstrate numeric-presentations in different cultures (locales).
"""
__author__ = "dn, IT&T Consultant"
__python__ = "3.12"
__created__ = "PyCharm, 02 Jan 2021"
__copyright__ = "Copyright © 2024~"
__license__ = "GNU General Public License v3.0"
# PSL
import locale
locales_to_compare = [
( "USA", "en_US", ),
( "France", "fr_FR", ),
( "Spain", "es_ES", ),
( "Portugal", "pt_PT", ),
( "Poland", "pl_PL", ),
]
print( "\n Country Integer Float" )
for country_name, locale_identifier in locales_to_compare:
locale.setlocale( locale.LC_ALL, locale_identifier, )
print( F"{country_name:>10}", end=" ", )
print(
locale.format_string("%10d", 123456, grouping=True, ),
end="",
)
print( locale.format_string("%15.2f", 123456.78, grouping=True, ) )
--
Regards =dn
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
ListAdmin: Is list/archive working correctly?
For example, have been following the thread "Is there a better way? [combining f-string, thousands separator, right align]". Me email (only) client shows a thread of 12 messages. The OP was @Gilmeh Serda (from an invalid email address). That appears in the email thread @Stefan Ram has had two contributions quoted, but no such original-message has appeared in the thread. The archive is only showing seven contributions (for some reason Grant's recent contribution under the different subject line: "Formatting a str as a number" appears separately, even though it threads as the same conversation in email) None of the OP's contributions appear! IIRC the design has been that it doesn't matter if a contribution comes from the Newsgroup or the email Discussion List, they are treated the same. Are Newsgroup contributions being archived (were they ever)? Is it user-error that some contributions don't appear on the list, but do appear in replies, or is there perhaps some other cause? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Script stops running with no error
he problem (and so that we don't have to read so much code in a bid to help) but that when you do ask for assistance you will be able to provide only the pertinent code AND some sample input-data with expected-results! (although, if all our dreams come true, you will answer your own question!) OK, is that enough by way of coding-tactics (not to mention the web-research) to keep you on-track for a while? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Is there a better way? [combining f-string, thousands separator, right align]
On 26/08/24 23:00, Dan Sommers via Python-list wrote:
On 2024-08-26 at 20:42:32 +1200,
dn via Python-list wrote:
and if we really want to go over-board:
RIGHT_JUSTIFIED = ">"
THOUSANDS_SEPARATOR = ","
s_format = F"{RIGHT_JUSTIFIED}{S_FIELD_WIDTH}{THOUSANDS_SEPARATOR}"
or (better) because right-justification is the default for numbers:
s_format = F"{S_FIELD_WIDTH}{THOUSANDS_SEPARATOR}"
To the extreme that if your user keeps fiddling with presentations (none
ever do, do they?), all settings to do with s_format could be added to a
config/environment file, and thus be even further separated from
program-logic!
And then you'll need a parser, many of whose Unique Challenges™ aren't
even apparent until you start parsing files from actual users, and
you'll still need some sort of fallback in the code anyway for the case
that s_format can't be parsed (for whatever reason).
Isn't a config file what just caused the global CrowdStrike outage? ;-)
That said, I understand that report generators are a thing, not to
mention RPG (https://en.wikipedia.org/wiki/IBM_RPG).
Okay, sorry; I'll just crawl back into the hole from whence I came.
Not at all. Please continue to question/ask/suggest!
This is a valid point. There are costs and benefits (trade-offs) to all
decisions!
That said, writing one's own parser would become a veritable can of
worms/rabbit hole. Here be dragons!
Similarly, explaining this takes longer than writing the example itself!
Older Windows users will know about .ini files, and Linux Admins are
familiar with .conf files. Many of us are already using JSON or YAML
formats. Any of these (and more) could be pressed into service, as
above. At the 'top end', there are also whole libraries devoted to
establishing application configuration or "environments": default
values, config files, command-line options, user-input...
Have switched to using Python-poetry, which replaces packaging methods
such as setuptools (as well as virtual-environment tools). It takes its
project configuration specifications from a pyproject.toml file. So, for
a few projects lately, I've been using .toml for application-config as
well. However, I have to say, this more from an attempt at consistency
than a decision of logic. (critique welcome)
That said, a setup.py configuration, took the form:
setup(
name='demo_project',
version='1.1.0',
packages=find_packages(),
install_requires=[
'requests',
'numpy',
...
],
entry_points={
...
Accordingly, it offers an example of the simplest format (for us), and
one which has a zero-learning pre-requisite. At execution-time, the
moment such a config is import-ed, a syntax-error will immediately bring
proceedings to a halt!
I have some stats-wonks as clients. They dabble in programming, but
(fortunately) realise their limitations. (usually!) The boss has had to
ban them from 'improving' my code ($paid to be an improvement on their
usual quality), but including a .py configuration/options file has
proven to be an honor-preserving compromise. Of course, they manage
their own runs, adjusting parameters as they go. So, any errors are
their own, and they can fix themselves (without anyone else knowing!).
Such would not work in many?most other environments - children: do not
try this at home!
An irritation for those of us who have to delve into projects after
they've been written, is a git-history full of the sorts of
user-tweaking changes vilified earlier. Putting user-config into a
separate file, even a separate sub-directory, makes it easy to spot
which updates to ignore, and thus, which to consider!
PS the reason why CrowdStrike was not the end of humanity as we know it,
(and only that of those who only know MSFT's eco-system) is because the
majority of the world's Internet servers run Linux - including Azure
(brings to mind the old saw: the package said "runs on Windows-95 or
better" so I installed it on Linux!)
Joking aside, we (virtuous ones) ALWAYS test BEFORE release. Correct?
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: Is there a better way? [combining f-string, thousands separator, right align]
On 26/08/24 03:12, Gilmeh Serda via Python-list wrote:
Subject explains it, or ask.
This is a bloody mess:
s = "123456789" # arrives as str
f"{f'{int(s):,}': >20}"
' 123,456,789'
With recent improvements to the expressions within F-strings, we can
separate the string from the format required. (reminiscent of FORTRAN
which had both WRITE and FORMAT statements, or for that matter HTML
which states the 'what' and CSS the 'how')
Given that the int() instance-creation has a higher likelihood of
data-error, it is recommended that it be a separate operation for ease
of fault-finding - indeed some will want to wrap it with try...except.
>>> s = "123456789" # arrives as str
>>> s_int = int( s ) # makes the transformation obvious and distinct
>>> s_format = ">20," # define how the value should be presented
>>> F"{s_int:{s_format}}"
' 123,456,789'
Further, some of us don't like 'magic-constants', hence (previously):
>>> S_FIELD_WIDTH = 20
>>> s_format = F">{S_FIELD_WIDTH},"
and if we really want to go over-board:
>>> RIGHT_JUSTIFIED = ">"
>>> THOUSANDS_SEPARATOR = ","
>>> s_format = F"{RIGHT_JUSTIFIED}{S_FIELD_WIDTH}{THOUSANDS_SEPARATOR}"
or (better) because right-justification is the default for numbers:
>>> s_format = F"{S_FIELD_WIDTH}{THOUSANDS_SEPARATOR}"
To the extreme that if your user keeps fiddling with presentations (none
ever do, do they?), all settings to do with s_format could be added to a
config/environment file, and thus be even further separated from
program-logic!
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: new here
It appears there were some delays in the email/servers. Thanks for this (and earlier) ideas and advice! On 23/08/24 17:38, rbowman via Python-list wrote: On Thu, 22 Aug 2024 19:56:54 -0700, Paul Rubin wrote: With MicroPython on the Pico, you use some command line utility to transfer files instead, but it is no big deal. Loading the UF2 is easy. https://www.raspberrypi.com/documentation/microcontrollers/ micropython.html I use VS Code with the MicroPython extension so when the board is plugged in it shows up as ttyACM0 or COM something I think on Windows. If you need a package for a peripheral the file structure on the actually device shows up so you can copy it to the lib directory. https://pypi.org/project/pipkin/ pipkin is the command line utility. Thonny isn't my favorite IDE but it does make life easy: https://projects.raspberrypi.org/en/projects/getting-started-with-the- pico/2 -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: new here
On 23/08/24 15:43, rbowman via Python-list wrote: On Fri, 23 Aug 2024 08:36:02 +1200, dn wrote: On 23/08/24 07:49, rbowman via Python-list wrote: On Thu, 22 Aug 2024 10:40:52 -0700, Paul Rubin wrote: The Pico uses MicroPython which is stuck on an old version of Python, unfortunately. How did this enter the conversation/thread? Paul's 'contribution' does not even appear on the Archive... I'm probably guilty. I mentioned in passing the older protocols like finger could even be implemented on something like the Pico W with MicroPython. The question arose because his message doesn't appear either in the conversation/email thread 'here', nor on the Archive. Perhaps not sent to the list? I am confused by the cross-over to Python-list. I only read/post to comp.lang.python. Is that echoed to Python-list or vice versa? As I understand it, posts to 'the list' may be made at comp.lang.python or by email. Once on the server, messages are reflected back to both. Thus, Thunderbird is not set-up to use the newsgroup and keeps complaining at me when it's asked to reply to both. So, all contributions (from me) enter the server via email. I haven't worked with CircuitPython lately and don't know if it has pulled in later features. Have you (gentle reader) used both and feel able to offer a comparison - when to prefer one over the other? I've only used CircuitPython on the Adafruit Playground Express. https://circuitpython.org/board/circuitplayground_express/ and MicroPython on the Pico W. Since then Adafruit has expanded their collection of boards and support them with CircuitPython. One difference that makes them hard to compare is the Express has quite a few on-board sensors like the Arduino Nano Sense 33, and interfaces to them are baked into CircuitPython. The Pico W has a wealth of I/O most doubling as I2C, PWM, or A/D with only a onboard LED for the mandatory 'hello world' blink code. MicroPython is more generic and you may have to import modules for specific external devices like the SSD1306 OLED display. That's easily done with Thonny or pipkin. Adding a display to the Pico-W is my next project... After that, gyros (am thinking it may not go so well, on balance... hah!). The Pico-W impresses. Its built-in Wi-Fi/Bluetooth capability makes life a lot easier (inside building use). Apart from the earlier comment, my biggest frustration has come from the lack of facilities in Thonny compared with PyCharm - but will pick-up skills there, no doubt. Conversely, (to having a separate radio-chip) I think I prefer the idea of being able to connect the Pico to whichever sensor(s) is/are actually-required. However, this is applied use - not learning or 'playing'. As far as core Python I'd say they're similar. MicroPython is more generic and may require more work to set up where Adafruit can match the boards they have developed. As I said it's been a while but MicroPython has the _threading module so you can utilize both cores of the RP2040. Adafruit's new Feather has a RP2040 and like the Pico W assumes you'll be using the PIO to externals rather than anything onboard so CircuitPython probably has it. https://www.adafruit.com/product/4884 From the horse's mouth: "There is great C/C++ support, unofficial (but really good) Arduino support, an official MicroPython port, and a CircuitPython port! We of course recommend CircuitPython because we think it's the easiest way to get started and it has support with most of our drivers, displays, sensors, and more, supported out of the box so you can follow along with our CircuitPython projects and tutorials." Whilst agreeing with the "easiest way to get started" claim, it probably also leads to the assumption that it will (later) be easier to run out of capability. Hence, that MicroPython would be the better professional option - assuming one already knows Python. Yes, a degree of 'comparing apples with oranges' - and a continually-moving target! I don't know if Adafruit has a RP2350 board yet but they say CircuitPython will be even happier on the Pico 2. https://www.adafruit.com/product/6006 No, out in the real-world, the Pico 2 is still vaporware. For better or worse there are a lot more choices now than fiddling around with the Arduino Uno back in the day. True. Hence the question. Thanks for the comments! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: new here
On 23/08/24 07:49, rbowman via Python-list wrote: On Thu, 22 Aug 2024 10:40:52 -0700, Paul Rubin wrote: The Pico uses MicroPython which is stuck on an old version of Python, unfortunately. How did this enter the conversation/thread? Paul's 'contribution' does not even appear on the Archive... I think it's up to 3.4 in general and erratic past that. It doesn't have the match from 3.10. I don't think it has f-strings though it may have the walrus. There are workarounds but it can be annoying. Two points: - it's cut-down to work on bare-metal which makes for low demands on resources, but commensurate shortage of the facilities we CPython developers take for-granted (ie may allow ourselves to find annoying) - it has f-strings, but frustrates those of us who prefer F-strings - the docs point-out that (compared with full-fat Python) it is less consistent across environments. Accordingly, worth reading the "Quick Reference for [your processor]" sections of the docs, eg R-Pi Pico version only has half of the ADC-methods. Once scale expectations to take into account the power of the processor, MicroPython goes-like-the-clappers! I haven't worked with CircuitPython lately and don't know if it has pulled in later features. Have you (gentle reader) used both and feel able to offer a comparison - when to prefer one over the other? [https://www.phrases.org.uk/meanings/like-the-clappers.html] -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: new here
On 22/08/24 09:15, Daniel via Python-list wrote: rbowman writes: On Tue, 20 Aug 2024 23:26:39 +0100, Daniel wrote: ... smolnet, as in things like Lesser used protocols not known by many in the mainstream. Such as: gopher, gemini, finger, spartan, titan, etc. An example of use, here's a weather service tied to a finger. Put your city name as the user. This isn't mine, but it is inspiring. Example: finger mi...@graph.no The OpSys on this machine no longer features finger (available for installation as an 'extra'). For Miami weather using a stock-standard web-browser, try: https://www.yr.no/en/content/2-4164138/meteogram.svg -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: new here
On 21/08/24 10:26, Daniel via Python-list wrote: Hi folks - New here. I've perused some posts and haven't seen a posting FAQ for this NG. I'm learning python right now to realize some hobby goals I have regarding some smolnet services. What are the NG standards on pasting code in messages? Do yall prefer I post a pastebin link if it's over a certain number of lines? I know this isn't IRC - just asking. Welcome Daniel! Despite some seeming to think of sending you elsewhere, there are a number of people 'here' who regularly volunteer their time to help others. As with any interaction, the quality of information in the question directly impacts what can be offered in-response. More of us can help with (pure) Python questions. Moving into specialised areas may reduce the number who feel competent to answer. We'll value any contribution you may be able to offer, and will look forward to hearing of the projects you attempt... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: bring back nntp library to python3
On 15/08/24 10:56, Alan Gauld via Python-list wrote: On 14/08/2024 23:32, Left Right via Python-list wrote: Lots of people care but the ability to influence these decisions seems to have been removed far from the general python user community. Python has moved from the BDFL/Bazaar to the Committee/Cathedral. Probably an inevitable consequence of its current "popularity". Perhaps in the ?good, old, days when Python was the small, scrappy language a strong community formed because there was a strong sense of "us" - as in, "us against the world". This atmosphere generates "cohesion" within the group. Does it (still) exist today? Where/when? Python is a victim of its own success. It is now used in so many different fields within computing it is not possible for one person to say "I use it all". Thus, when someone says (s)he is a "Python Programmer" what is meant is most-likely one of web/front-end work, back-end/server/networking, data science, machine learning, etc. As a PUG-Leader, this a daunting part of trying to generate and keep 'community'. 'Data science people' won't attend 'web' meetings (by-and-large), and vice-versa - indeed some even feel the 'right' to moan that some other area of Python happens to be the topic for the next meeting. The converse view (which is seldom well-taken if offered as a riposte to such complaints) is that if folk volunteer in some way, their efforts will (most likely) be embraced with gratitude - but how many do make such offers/participate in a practical fashion! Whither community? Cohesion? Thus, a grave difficulty for leaders who are unable to see these sorts of concerns - and act accordingly. A shift that should have occurred within steering groups as Python grew in popularity, was to add applications-expertise to the central group of Core Maintainers. However, unless there is trust and respect between members, one may be (too) quick to reject comments and ideas from 'another'. Perhaps Python's state-of-democracy is heavily influenced by nation-state politics, where the desire for division seems to be overwhelming ideas of community/society? How does such benefit community - those represented? Growth and size will inevitably require adaption. Almost inevitably it brings 'structure'. Whereas some do care (per @Alan's point), the average Python-programmer probably doesn't understand the current structures, and might even eschew such/reject their need. How does this fit with "community"? What is personal-responsibility? What channels should folk be using? Are members of the community feeling 'heard'? If a committee perceives themselves besieged, the tendency is to look inwards and become determinedly-defensive - which, in cases like this, is likely the exact opposite of what the decision's opponents desire! How should a 'community' handle such? How should decisions be made, and then communicated in such a way as to promote and build community, even though some members may be disappointed? Recently there was an election for PSF members. Did 'everyone' participate? What decision-making processes are usable in the face of such large numbers - and how seriously are/would they be taken by 'the average Python user'? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Help needed - - running into issues with python and its tools
On 4/08/24 09:34, o1bigtenor via Python-list wrote: On Sat, Aug 3, 2024 at 4:06 PM dn via Python-list wrote: On 4/08/24 08:17, o1bigtenor via Python-list wrote: Greetings Looking at ESP8266 and wanting to program it using micropython (really don't want to have to learn C++ (not enough hours in the day as it is!!)). One of the tools I need to be able to use is esptools - - well in the devuan world you need to run that on either Devaun 3 or 5 - - - its just not available on devuan 4. Tried installing all the tools I need using downloads and .deb installs but then I need to have python3.12 and that's also not part of Devuan4. Not versed enough to set up a good venv (if that's possible) so that I could work in that specific venv and have my cake (and get to eat it too (grin!). Suggestions - - - ideas - - - please? Sorry if this offends, but this is a list of short-cuts and reasons why they don't work (immediately). Have just come from a discussion about 'how to start a project'. Amongst the questions to ask are: "what resources do we have (or can add) to achieve?". Fair question details interleaved - - - In this case, if Python-skill is a "personnel-resource" (and C++ a "constraint"), will question the ESP over Raspberry Pi (say)? Well - - - RPi world technical specs is usable from -20 to 60 C (iirc on the top number) and for my project I absolutely need to have usability to at least -40 - - could possibly do a bit less but -35 C is a hard requirement so the RPi and Pico (which I would like to use) is out but ESP8266 runs in that -40 to 65 C range. Interesting, but creates a mis-match of tools - battles for you to fight... Why talking of Python 3.12 when the solution involves MicroPython? Because one uses psytool on one computer to transfer a program to the MicroPython system. In fact there are a set of tools that need Python3.12 to be able to do this and therefore the question. Perhaps need to take a step back and look at 'options' - relate needs to resources, and evaluate the impact of each decision on later ones - as well as against your personal skills (modify objectives to limits, or accept that some learning/training will be necessary as pre-requisite to (being able to) attack the project). I have been investigating using a venv but am not finding clear directions so that I could set up Python3.12 inside (along with the other needed tools). The more I'm looking the less useful most of the information I'm finding is becoming. Therefore I thought I would go to the python gurus for information - - - which I have. So please - - - how do I set up a venv so that I can install and run python 3.12 (and other needed programs related to 3.12) inside? If you mean venv itself, which "directions" have you reviewed? This one (https://python.land/virtual-environments/virtualenv) seems very straight-forward and shows "What's inside a venv?" to include python.exe. Given that venv is more-or-less the official/traditional solution, what are you doing differently - perhaps the question is lacking detail. (see also @Cameron's take) Personally, I'm using Poetry (https://python-poetry.org) which seemed just as easy to pick-up; plus pyenv to maintain multiple versions of Python on one machine. -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Help needed - - running into issues with python and its tools
On 4/08/24 08:17, o1bigtenor via Python-list wrote: Greetings Looking at ESP8266 and wanting to program it using micropython (really don't want to have to learn C++ (not enough hours in the day as it is!!)). One of the tools I need to be able to use is esptools - - well in the devuan world you need to run that on either Devaun 3 or 5 - - - its just not available on devuan 4. Tried installing all the tools I need using downloads and .deb installs but then I need to have python3.12 and that's also not part of Devuan4. Not versed enough to set up a good venv (if that's possible) so that I could work in that specific venv and have my cake (and get to eat it too (grin!). Suggestions - - - ideas - - - please? Sorry if this offends, but this is a list of short-cuts and reasons why they don't work (immediately). Have just come from a discussion about 'how to start a project'. Amongst the questions to ask are: "what resources do we have (or can add) to achieve?". In this case, if Python-skill is a "personnel-resource" (and C++ a "constraint"), will question the ESP over Raspberry Pi (say)? Why talking of Python 3.12 when the solution involves MicroPython? Perhaps need to take a step back and look at 'options' - relate needs to resources, and evaluate the impact of each decision on later ones - as well as against your personal skills (modify objectives to limits, or accept that some learning/training will be necessary as pre-requisite to (being able to) attack the project). -- Regards =dn -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Predicting an object over an pretrained model is not working
On 31/07/24 06:18, marc nicole via Python-list wrote: Hello all, I want to predict an object by given as input an image and want to have my model be able to predict the label. I have trained a model using tensorflow based on annotated database where the target object to predict was added to the pretrained model. the code I am using is the following where I set the target object image as input and want to have the prediction output: ... WHile I expect only the dict to contain the small_ball key How's that is possible? where's the prediction output?How to fix the code? To save us lots of reading and study to be able to help you, please advise: 1 what are the meanings of all these numbers? 'sheep': [[233.0, 92.0, 448.0, -103.0, 5.3531270027160645], [167.0, 509.0, 209.0, 101.0, 4.947688579559326], [0.0, 0.0, 448.0, 431.0, 3.393721580505371]] 2 (assuming it hasn't) why the dict has not been sorted into a meaningful order 3 how can one tell that the image is more likely to be a sheep than a train? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Best use of "open" context manager
On 6/07/24 22:49, Rob Cliffe via Python-list wrote:
Consider this scenario (which I ran into in real life):
I want to open a text file and do a lot of processing on the lines
of that file.
If the file does not exist I want to take appropriate action, e.g.
print an error message and abort the program.
I might write it like this:
try:
with open(FileName) as f:
for ln in f:
print("I do a lot of processing here")
# Many lines of code here .
except FileNotFoundError:
print(f"File {FileName} not found")
sys.exit()
but this violates the principle that a "try" suite should be kept small,
so that only targeted exceptions are trapped,
Yes!
not to mention that having "try" and "except" far apart decreases
readability.
Uh-oh!
- and there's a bit of a hang-over for old-timers who had to take care
of file-locking within the application - we try to minimise 'time'
between opening a file and closing it (etc)!
As it seems the file is opened to read. Less relevant in this case, but
habits and styles of coding matter...
Or I might write it like this:
try:
f = open(FileName) as f:
FileLines = f.readlines()
except FileNotFoundError:
print(f"File {FileName} not found")
sys.exit()
# I forgot to put "f.close()" here -:)
for ln in File Lines:
print("I do a lot of processing here")
# Many lines of code here .
but this loses the benefits of using "open" as a context manager,
and would also be unacceptable if the file was too large to read into
memory.
So, now there are two concerns:
1 FileNotFoundError, and
2 gradual processing to avoid memory-full
- added to remembering to close the file.
Really I would like to write something like
try:
with open(FileName) as f:
except FileNotFoundError:
print(f"File {FileName} not found")
sys.exit()
else: # or "finally:"
for ln in f:
print("I do a lot of processing here")
# Many lines of code here .
but this of course does not work because by the time we get to "for ln
in f:" the file has been closed so we get
ValueError: I/O operation on closed file
I could modify the last attempt to open the file twice, which would
work, but seems like a kludge (subject to race condition, inefficient).
Is there a better / more Pythonic solution?
Idea 1: invert the exception handling and the context-manager by writing
a custom context-manager class which handles FileNotFoundError
internally. Thus, calling-code becomes:
with...
for...
processing
Idea 2: incorporate idea of encapsulating "processing" into a
(well-named) function to shorten the number of lines-of-code inside the
with-suite.
Idea 3: consider using a generator to 'produce' lines of data
one-at-a-time. Remember that whilst context-managers and generators are
distinct concepts within Python, they are quite similar in many ways.
So, a custom generator could work like a context-manager or 'wrap' a
context-manager per Idea 1.
Building a custom-class (Idea 1 or Idea 3) enables the components to be
kept together, per the ideal. It keeps the try-except components close
and easy to relate. It is Pythonic (in the OOP style).
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: Anonymous email users
On 25/06/24 05:17, Thomas Passin via Python-list wrote: On 6/24/2024 5:51 AM, Barry Scott via Python-list wrote: On 23 Jun 2024, at 06:58, Sebastian Wells via Python-list wrote: The spammers won the spam wars, so even if you have someone's real e-mail address, that's no guarantee that you can contact them. You certainly wouldn't be able to contact me at my real e-mail address, unless you also had my phone number, so you could call me and tell me that you sent me an e-mail, and what the subject line was so I can find it. I don't even open my e-mail inbox unless there's a specific message I'm expecting to find there right now. My email address is well known and yes I get spam emails. I use the wonderful python based spambayes software to detect spam and file into a Junk folder. It works for 99.9% of the emails I get. I use the Thunderbird mail client and I just use its built in spam detector. I don't know how it works but it's pretty darn good. Very few false positives or false negatives. And it learns each time I classify a message as "Junk", in case it missed one. I am subscribed to a lot of mailing lists. I just checked and I am getting ~3,200 emails a month of which less than 200 are spam. A few years ago the spam count was greater than a 1,000 a month. I have been using spambayes for a very long time, 20 years I guess at this point and bayesian categorisation has stood the test of time for me. For me the spammers have not won, I have the tech to keep ahead of them. Aside from the attractions of the new, and the 'shiny', what email-antagonists didn't anticipate, was that as fast as they moved to non-email messaging, the spammers, advertisers, and malcontents would simply do the same. Thus, a variation on whack-a-mole, as folk move from platform to platform trying to stay-ahead and find an illusion of safety. Quite how one out-runs human-nature is an issue philosophised-over by the (Ancient) Greeks (and was no-doubt old even-then). Paradoxically, applying for an account elsewhere usually involves providing an email address. Even backing-up a cell-phone (communication tool) to the cloud requires an email address(!!!) Most of the non-email platforms are provided by organisations who have 'other uses' for your personal-data (and not forgetting GMail and MSFT's email services). Python mailing-lists are covered by the Code of Conduct and monitored by ListAdmins. Thus, there are controls which limit the impact which advertisers and others with non-pythonic aims might otherwise exert! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Anonymous email users
On 18/06/24 05:29, Roel Schroeven via Python-list wrote: AVI GROSS via Python-list schreef op 17/06/2024 om 17:03: I simply am thinking that people who do not allow me to easily reply to them directly, should be ignored by me and not get my cooperation that way. FWIW, personally I (mostly) don't see the point of replying to people personally. To me a public mailing list is much like any public forum, where my expectation is that conversations happen in public. To me it always feels weird when I get a personal reply when I make a public post in a mailing list. I mostly ignore those, unless there's really something in it that's best kept out of the public. Sometimes people write long mails with wandering thoughts only loosely related to the topic at hand directly to me instead of to the whole list. My take is: if it's not on-topic enough for the list, it's not on-topic enough for me either. Not that it bothers me *that* much; I just ignore those. It's very well possible that's just me, and that other people have different expectations. +1 The "public" part is not to embarrass posters, but recognition that there are likely other people 'out there' (or arriving in-future if they care to read the archives) experiencing a similar problem. (hence need for descriptive Subject lines - isn't the most difficult task in programming 'choosing names'?) Yes, like @Avi, I have been known to contact folk directly. However, such for personal purposes - as distinct from the list, and possibly subjects OT for the list. When contacted by others off-list, I play it by ear - ignore, personal, or post response on-list. (some lists/email-clients do seem to prefer personal replies, even when incoming message is from a list - so easy accident.) The Delete-key is your friend! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Anonymous email users
On 15/06/24 10:00, AVI GROSS via Python-list wrote: I notice that in some recent discussions, we have users who cannot be replied to directly as their email addresses are not valid ones, and I believe on purpose. Examples in the thread I was going to reply to are: ... It's an interesting conundrum. There are good reasons and nefarious, for such behavior. Some have questioned my behavior in similar regard - asking why I use initials (also used IRL). It is because my first name "David" is/was very popular. At a meeting this week there were three of us. Thus, "David", "Dave", and "dn" was necessary to distinguish between us. These mailing-lists all run under the Python Code of Conduct. This also effects a conundrum. Firstly, that someone abusing others (for example) shall be held responsible. Secondly, that in order to hold someone responsible, he/she/... must be identifiable. Personal opinion: if someone is asked a question/clarification/sample-code, particularly as a response to their own OP, and does not answer; this is at the least rude, and thus disrespectful, or at worst grounds for not bothering with them again - hardly a 'community' attitude! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: From JoyceUlysses.txt -- words occurring exactly once
On 31/05/24 14:26, HenHanna via Python-list wrote: On 5/30/2024 2:18 PM, dn wrote: On 31/05/24 08:03, HenHanna via Python-list wrote: Given a text file of a novel (JoyceUlysses.txt) ... could someone give me a pretty fast (and simple) Python program that'd give me a list of all words occurring exactly once? -- Also, a list of words occurring once, twice or 3 times re: hyphenated words (you can treat it anyway you like) but ideally, i'd treat [editor-in-chief] [go-ahead] [pen-knife] [know-how] [far-fetched] ... as one unit. Split into words - defined as you will. Use Counter. Show some (of your) code and we'll be happy to critique... hard to decide what to do with hyphens and apostrophes (I'd, he's, can't, haven't, A's and B's) 2-step-Process 1. make a file listing all words (one word per line) 2. then, doing the counting. using from collections import Counter Apologies for lateness - only just able to come back to this. This issue is not Python, and is not solved by code! If you/your teacher can't define a "word", the code, any code, will almost-certainly be wrong! One of the interesting aspects of our work is that we can write all manner of tests to try to ensure that the code is correct: unit tests, integration tests, system tests, acceptance tests, eye-tests, ... However, there is no such thing as a test (or proof) that statements of requirements are complete or correct! (nor for any other previous stages of the full project life-cycle) As coders we need to learn to require clear specifications and not attempt to read-between-the-lines, use our initiative, or otherwise 'not bother the ...'. When there is ambiguity, we should go back to the user/client/boss and seek clarification. They are the domain/subject-matter experts... I'm reminded of a cartoon, possibly from some IBM source, first seen in black-and-white but here in living-color: https://www.monolithic.org/blogs/presidents-sphere/what-the-customer-really-wants That has been the sad history of programming and dev.projects - wherein we are blamed for every short-coming, because no-one else understands the nuances of development projects. If we don't insist on clarity, are we our own worst enemy? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: From JoyceUlysses.txt -- words occurring exactly once
On 31/05/24 08:03, HenHanna via Python-list wrote: Given a text file of a novel (JoyceUlysses.txt) ... could someone give me a pretty fast (and simple) Python program that'd give me a list of all words occurring exactly once? -- Also, a list of words occurring once, twice or 3 times re: hyphenated words (you can treat it anyway you like) but ideally, i'd treat [editor-in-chief] [go-ahead] [pen-knife] [know-how] [far-fetched] ... as one unit. Did you mention the pay-rate for this work? Split into words - defined as you will. Use Counter. Show some (of your) code and we'll be happy to critique... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: SOLVED! Re: Weird Stuff (Markdown, syntax highlighting and Python)
On 29/05/24 06:49, Gilmeh Serda via Python-list wrote: Solved by using a different method. Hedonist for hire... no job too easy! This combination of sig-file and content seems sadly ironic. How about CONTRIBUTING to the community by explaining 'the solution' to people who may find a similar problem - in the similar manner to the various members who have helped YOU, voluntarily (and despite the paucity of source-information and response)? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Weird Stuff (Markdown, syntax highlighting and Python)
With reference to another reply here, the "Weird stuff" came from
reading the question, finding it unclear, and only later realising that
whereas most people write Markdown-formatted documents for later
processing, or perhaps docstrings in Markdown-format for collection by
documentation systems; here, the objective appears to be using Python to
generate Markdown.
How much have you used Markdown to any serious degree, before attempting
this feat?
On 26/05/24 18:28, Gilmeh Serda via Python-list wrote:
The web claims (I think on all pages I've read about Markdown and Python)
that this code should work, with some very minor variants on the topic:
There are so many "variants", the problem is not "minor"!
Markdown users learn to use their tool (again, see @Grant's question)
and work within the implementation of that "variant".
Like any other non-standardised tool, the users of some particular
'version' often fail to realise that others using different versions may
not enjoy the same experience. Plus-one for standardisation!
At the end of the message, the web.refs reveal use of a package which is
based upon a variant of Markdown that is 20-years old(!), albeit with
some updates to suit yet another variant. Neither variant-author famous
for collaboration. The phrase YMMV springs to mind...
Some ten years ago, an effort was made to standardise Markup, and it
ended-up being called CommonMark. Why is it not called "Standard
Markdown" one might ask? Because the fellow who 'invented' Markdown
objected. This very objection has likely led directly to your
confusions, because the particular PyPi package is based upon that
original definition...
Whereas, Markdown 3.6 is the most-recently updated Markdown search-hit
on PyPi today, have you tried any of the others (which, ironically, may
offer more recent and/or more standardised coverage)?
This has worked in all of the Markdown processors I have used or tried-out:
The (?reasonable) 'common-core', offers single back-ticks for code,
triple back-ticks for a code-block, and the latter with or without a
language specification which *usually* kicks-in syntax highlighting.
```python
import os
with open(os.path.join('/home/user/apath', 'somefile')) as f:
print(f.read())
```
However, that is not the case. At least not for me (using Python 3.12.3).
It's not Python 3 that is the problem. It is the "Markdown 3.6" package!
If instead I type it:
I've not seen the hash-bang combination in-the-wild (but YMMV!)
#!python
import os
with open(os.path.join('/home/user/apath', 'somefile')) as f:
print(f.read())
As an indented block (four spaces) and a shebang, THEN it works. You even
get line numbers by default.
An indented-block is NOT necessarily the same as a code-block - just as
"code" is not necessarily "Python".
Line numbers are great - although if a code snippet is extracted from
the middle of some example code-file, the original line-numbers won't
line-up with Markdown's...
N.b. if you don't know, you also need to generate a css file using
pygments to make this work.
That's not what the package's docs suggest:
https://python-markdown.github.io/extensions/fenced_code_blocks/
Not until I started to read the markdown source code and its docs pages,
the coin dropped.
I'm posting this for other Markdown newbies that otherwise probably would
spend hours trying to make it work.
Speaking of Markdown. Does anybody out there have any idea how to turn on
table borders, adjust them (color/width/etc.) and such things? Currently I
have to add HTML to do so, which works, but isn't very nice. I'd hate to
spend an additional day or two, hunting for this info.
Again, heavily dependent upon the tool in-use. For example, most SSGs
and doc-tools (which accept Markdown) have a .css or theming-system
which enables 'decorations'.
References:
https://pypi.org/project/Markdown/
https://python-markdown.github.io/
Further reading:
https://en.wikipedia.org/wiki/Markdown
https://commonmark.org
https://pypi.org/search/?q=markdown
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: Cprod -- (writing this: itertools.product([0, 1], repeat=N )
On 22/05/24 07:14, HenHanna via Python-list wrote: How can i write this function Cprod (Cartesian Product) simply? (writing this out: itertools.product([0, 1], repeat=N ) The value can be a list or a Tuple. cprod([0, 1], 1) => ((0) (1)) cprod([0, 1], 2) => ((0,0) (0,1) (1,0) (1,1)) This works: def cprod(x, c): if c==1: return [[i] for i in x] Sub= cprod(x, c-1) return [i for F in x for i in [[F]+R for R in Sub]] -- Is there another way to write [F]+R ??? Other ways to improve it? https://python.readthedocs.io/en/stable/library/itertools.html#itertools.product -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Data Ethics (Virtual) Meeting
Virtual meeting, Wed 17 April, 1800 for 1830 (NZST, ie 0630 UTC) Data Ethics Emma McDonald is the Director of the Interim Centre for Data Ethics and Innovation at Stats NZ (New Zealand Government Department of Statistics) Emma will talk about why Stats NZ is establishing a Centre for Data Ethics and Innovation, and why it needs to be set up as a network that draws on and leverages knowledge and expertise across relevant work programmes and people across agencies. As an initiative, the Centre is there to help agencies develop and maintain secure and trusted data environments. A large part of this is drawing on a diverse network of people who can support the with sharing the importance of data ethics being a critical component of data driven technologies. Will be of-interest to Quants, Data Science, and Machine Learning folk; as well as those of us with wider interest in what should/not happen with personal, public, and corporate data... She will be wanting to hear what folk have to say, and is interested to recruit competent individuals for hui*, consultations, and the like. WebRef: https://data.govt.nz/leadership/the-interim-centre-for-data-ethics-and-innovation/ from which you can access their Work Programme and Guidance developed to-date. Please RSVP at https://www.meetup.com/nzpug-auckland/events/299764076/ * hui is the Te Reo Maori word for meeting or conference (Te Reo is one of New Zealand's official languages) -- Regards =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: How to Add ANSI Color to User Response
On 11/04/24 06:50, WordWeaver Evangelist via Python-list wrote: I have a simple question. I use the following textPrompt in some of my Jython modules: '\n[1;33mYour choice is? (A B C D E): ', maxChars=1, autoAccept=False, forceUppercase=True) Is there a way to add an ANSI color code to the end where the conditions are, so that the color of the user’s input is of a color of my choosing, instead of just white? Thank you very much in advance. Kind regards, Bill Kochman Haven't tried using any of theses techniques, but may define input() color, as well as print():- How to print colored terminal text in Python MAR 06, 2024 ... https://byby.dev/py-print-colored-terminal-text -- Regards =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Multiplication
The April Fools joke was on those of us who never received/have yet to receive @Stefan's OP. On 2/04/24 08:02, Avi Gross via Python-list wrote: Is this a April 1 post for fools. Multiplication with an asterisk symbol is built into python. The same symbol used in other contexts has other contexts has an assortment of largely unrelated meanings such as meaning everything when used to import. On Mon, Apr 1, 2024, 1:27 PM Piergiorgio Sartor via Python-list < python-list@python.org> wrote: On 01/04/2024 10.40, Stefan Ram wrote: Q: How can I multiply two variables in Python? I tried: a = 2 b = 3 print( ab ) but it did not work. A: No, this cannot work. To multiply, you need the multiplication operator. You can import the multiplication operator from "math": Code example: from math import * a = 2 b = 3 print( a * b ) I guess the operator "*" can be imported from any module... :-) bye, -- piergiorgio -- https://mail.python.org/mailman/listinfo/python-list -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: MTG: Introductions to PyQt and DataClasses
On 18/03/24 10:02, Jim Schwartz wrote: Actually, I have a sleep disorder that requires me to keep a constant sleep schedule. Thats why I asked. At a weekend meeting, discussion swirled around topics such as the best way to learn/work, how much work we should attempt in one sitting, could/should I 'do more', and similar. One of the valuable observations is that most of us would benefit by improving our sleep-schedule and ensuring we do sleep for sufficient time (probably longer than current habit). -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Configuring an object via a dictionary
On 18/03/24 04:11, Peter J. Holzer via Python-list wrote: On 2024-03-17 17:15:32 +1300, dn via Python-list wrote: On 17/03/24 12:06, Peter J. Holzer via Python-list wrote: On 2024-03-16 08:15:19 +, Barry via Python-list wrote: On 15 Mar 2024, at 19:51, Thomas Passin via Python-list wrote: I've always like writing using the "or" form and have never gotten bit I, on the other hand, had to fix a production problem that using “or” introducted. I avoid this idiom because it fails on falsy values. Perl has a // operator (pronounced "err"), which works like || (or), except that it tests whether the left side is defined (not None in Python terms) instead of truthy. This still isn't bulletproof but I've found it very handy. So, if starting from: def method( self, name=None, ): rather than: self.name = name if name else default_value ie self.name = name if name is True else default_value These two lines don't have the same meaning (for the reason you outlined below). The second line is also not very useful. the more precise: self.name = name if name is not None or default_value or: self.name = default_value if name is None or name Those are syntax errors. I think you meant to write "else" instead of "or". Yes, exactly. That's the semantic of Perl's // operator. JavaScript has a ?? operator with similar semantics (slightly complicated by the fact that JavaScript has two "nullish" values). Thanks Peter! (yes, sad consequences of suffering a neighbor's party-til-midnight followed by an 0530 meeting-start - children: don't code exhausted!) Herewith, an illustration of how the corrected version of the above works - and how (in what seem unusual cases) it avoids any truthy/falsy confusion, as raised earlier in this thread: >>> default_value = "default" >>> name = "Fred Flintstone" >>> name if name is not None else default_value 'Fred Flintstone' >>> name = None >>> name if name is not None else default_value 'default' >>> name = False >>> name if name is not None else default_value False >>> name = 1 >>> name if name is not None else default_value 1 >>> name = 0 >>> name if name is not None else default_value 0 Personally: I find the above coding more logical, because our primary interest is on 'the happy case', ie where the value has been assigned (to "name"); and the default_value is only applied as a "guard". On the other hand, I dislike the not-condition because it forces me to think (and maybe dust-off DeMorgan). Accordingly: >>> name = "Fred Flintstone" >>> default_value if name is None else name 'Fred Flintstone' >>> name = None >>> default_value if name is None else name 'default' >>> name = False >>> default_value if name is None else name False ... YMMV! NB your corporate Style Guide may prefer 'the happy path'... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: MTG: Introductions to PyQt and DataClasses
On 17/03/24 23:40, Jim Schwartz wrote: Will it be recorded? Better than that (assumption) "coming soon" - please join-up or keep an eye on PySprings' Meetup ANNs: https://www.meetup.com/pysprings/ On Mar 17, 2024, at 1:47 AM, dn via Python-list wrote: The Auckland Branch of NZPUG meets this Wednesday, 20 March at 1830 NZDT (0530 UTC, midnight-ish Tue/Wed in American time-zones), for a virtual meeting. Part 1: Learn the basics of PyQt with code examples. Hannan Khan is currently consulting as a Data Scientist for the (US) National Oceanic and Atmospheric Administration. He holds a Bachelor's degree in Neuroscience as well as a Masters in Computer Science. As a keen member of the PySprings Users' Group (Colorado), his contribution is part of a collaboration between our two PUGs. Part 2: Why use Dataclasses? - will be the question asked, and answered, by yours truly. After surveying a number of groups, it seems most of us know that Dataclasses are available, but we don't use them - mostly because we haven't ascertained their place in our tool-box. By the end of this session you will, and will have good reason to use (or not) Dataclasses! Everyone is welcome from every location and any time-zone. The NZPUG Code of Conduct applies. JetBrains have kindly donated a door-prize. Our BigBlueButton web-conferencing instance is best accessed using Chromium, Brave, Vivaldi, Safari, etc, (rather than Firefox - for now). A head-set will facilitate asking questions but text-chat will be available. Please RSVP at https://www.meetup.com/nzpug-auckland/events/299764049/ See you there! =dn, Branch Leader -- https://mail.python.org/mailman/listinfo/python-list -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
MTG: Introductions to PyQt and DataClasses
The Auckland Branch of NZPUG meets this Wednesday, 20 March at 1830 NZDT (0530 UTC, midnight-ish Tue/Wed in American time-zones), for a virtual meeting. Part 1: Learn the basics of PyQt with code examples. Hannan Khan is currently consulting as a Data Scientist for the (US) National Oceanic and Atmospheric Administration. He holds a Bachelor's degree in Neuroscience as well as a Masters in Computer Science. As a keen member of the PySprings Users' Group (Colorado), his contribution is part of a collaboration between our two PUGs. Part 2: Why use Dataclasses? - will be the question asked, and answered, by yours truly. After surveying a number of groups, it seems most of us know that Dataclasses are available, but we don't use them - mostly because we haven't ascertained their place in our tool-box. By the end of this session you will, and will have good reason to use (or not) Dataclasses! Everyone is welcome from every location and any time-zone. The NZPUG Code of Conduct applies. JetBrains have kindly donated a door-prize. Our BigBlueButton web-conferencing instance is best accessed using Chromium, Brave, Vivaldi, Safari, etc, (rather than Firefox - for now). A head-set will facilitate asking questions but text-chat will be available. Please RSVP at https://www.meetup.com/nzpug-auckland/events/299764049/ See you there! =dn, Branch Leader -- https://mail.python.org/mailman/listinfo/python-list
Re: Configuring an object via a dictionary
On 17/03/24 12:06, Peter J. Holzer via Python-list wrote: On 2024-03-16 08:15:19 +, Barry via Python-list wrote: On 15 Mar 2024, at 19:51, Thomas Passin via Python-list wrote: I've always like writing using the "or" form and have never gotten bit I, on the other hand, had to fix a production problem that using “or” introducted. I avoid this idiom because it fails on falsy values. Perl has a // operator (pronounced "err"), which works like || (or), except that it tests whether the left side is defined (not None in Python terms) instead of truthy. This still isn't bulletproof but I've found it very handy. So, if starting from: def method( self, name=None, ): rather than: self.name = name if name else default_value ie self.name = name if name is True else default_value the more precise: self.name = name if name is not None or default_value or: self.name = default_value if name is None or name because "is" checks for identity, whereas "==" and True-thy encompass a range of possible alternate values? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Configuring an object via a dictionary
On 16/03/24 21:15, Barry via Python-list wrote: On 15 Mar 2024, at 19:51, Thomas Passin via Python-list wrote: I've always like writing using the "or" form and have never gotten bit I, on the other hand, had to fix a production problem that using “or” introducted. I avoid this idiom because it fails on falsy values. As with any other facility, one has to understand ALL implications! It must be one of those intensely-frustrating errors to track-down, which is then oh-so-simple to fix! Are you able to list (real, if suitably anonymised) examples of where the truthy/falsy was inappropriate, please? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Configuring an object via a dictionary
ss.__init__( self, config, ) might be something like: ( self.source_name, self.server_host, self.server_port, self.user_base, self.user_identifier, self.group_base, self.group_identifier, self.owner_base = config_access() ) If you know my style/preferences, notice that I'm breaking my own 'rule' of using named-parameters in preference to positional-parameters when there are three or more. However, this *may* be one of those exceptions (cf hobgoblins). That said, this is the third and least-preferred idea! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: A Single Instance of an Object?
Good question Rambius!
On 12/03/24 09:53, Ivan "Rambius" Ivanov via Python-list wrote:
Hello,
I am refactoring some code and I would like to get rid of a global
variable. Here is the outline:
import subprocess
CACHE = {}
First thought: don't reinvent-the-wheel, use lru_cache
(https://docs.python.org/3/library/functools.html)
The global cache variable made unit testing of the lookup(key) method
clumsy, because I have to clean it after each unit test. I refactored
it as:
class Lookup:
def __init__(self):
self.cache = {}
Change "cache" to be a class-attribute (it is currently an instance.
Then, code AFTER the definition of Lookup can refer to Lookup.cache,
regardless of instantiation, and code within Lookup can refer to
self.cache as-is...
--
Regards,
=dn
--
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Re: Variable scope inside and outside functions - global statement being overridden by assignation unless preceded by reference
On 7/03/24 05:28, Jacob Kruger via Python-list wrote: ... So, yes, know this comes across like some form of a scam/joke, or list-garbage, since it doesn't make any sense to me at all, but still just wondering if missing something, or should I shift over to 3.12 to see if if works differently, or just try reinstalling 3.11 from scratch, or should I retry the above in something like the VS code console, or a different python console, etc.? Some of the facts, such as HOW the code was being executed were missing (see earlier request for a cut-down scenario, AND reports from others saying 'but it works for me'). The idea of importing a module into the REPL and then (repeatedly) manually entering the code to set-up and execute is unusual (surely type such into a script (once), and run that (repeatedly). As you say, most of us would be working from an IDE and hitting 'Run'. Am wondering why you weren't - but it's not important. That said, the REPL is the perfect place to learn, experiment, and prototype - particularly when compared with the facilities of other language's eco-systems. The entirety of the on-line Tutorial cannot be wrong! (although, after a quick review, I've failed to see where the Tutorial mentions the usual development mode, apart from two very brief asides (the most useful is almost at the very end(?)) - but then (as they say) the objective is to show the language! The lesson-learned is that there are different 'environments' and different ways of building the environment in which the code will run. That's a valuable lesson, and full of subtlety! Glad to see that comparing id()s was useful - for diagnosis but not solution. Other tools might include the locals() and globals() functions. You may also have detected that many of us try to avoid globals and the implicit assumptions about the behavior of mutable collections (eg lists) when treated as 'global'. Then there are "closures", the "LEGB" rule, namespaces, scope, and ... -- -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Variable scope inside and outside functions - global statement being overridden by assignation unless preceded by reference
Jacob, Please reduce the problem to a small code-set which reproduces the problem. If we can reproduce same, then that tells us something. At the very least, we can experiment without having to expend amounts of time in a (likely faulty) bid to reproduce the same environment. Also, code is the ultimate description! Perhaps start with a small experiment: - after l_servers is created, print its id() - after the global statement, print its id() - after the clear/reassignment, print its id() Is Python always working with the same list? Please advise... On 6/03/24 07:13, Jacob Kruger via Python-list wrote: Hi there Working with python 3.11, and, issue that confused me for a little while, trying to figure out what was occurring - unless am completely confused, or missing something - was that, for example, when having pre-defined a variable, and then included it in the global statement inside a function, that function was still referring to a completely local instance, without manipulating outside variable object at all unless I first executed a form of referral to it, before then possibly assigning a new value to it. Now, this does not seem to occur consistently if, for example, I just run bare-bones test code inside the python interpreter, but consistently occurs inside my actual testing script. Basically, in a file with python code in that am using for a form of testing at the moment, at the top of the file, under all the import statements, I initiate the existence of a list variable to make use of later: # code snippet l_servers = [] # end of first code snippet Then, lower down, inside a couple of different functions, the first line inside the functions includes the following: # code snippet global l_servers # end code snippet That should, in theory, mean that if I assign a value to that variable inside one of the functions, it should reflect globally? However, it seems like that, while inside those functions, it can be assigned a new list of values, but if I then return to the scope outside the functions, it has reverted back to being an empty list = []? The issue seems to specifically (or not) occur when I make a call to one function, and, in the steps it's executing in one context, while it's not doing anything to the list directly, it's then making a call to the second function, which is then meant to repopulate the list with a brand new set of values. Now, what almost seems to be occurring, is that while just manipulating the contents of a referenced variable is fine in this context, the moment I try to reassign it, that's where the issue is occurring . Here are relevant excerpts from the file:- # start code # original assignation in main part of file l_servers = [] # function wich is initially being executed def interact(): global l_servers # extra code inbetween choosing what to carry out # ... # end of other code bl_response, o_out = list_servers() if bl_response: # just make sure other function call was successful l_servers.clear() # first make reference to global variable for srv in o_out: l_servers.append(srv) # now re-populate items # end code snippet from inside interact function # end of interact function # end of code snippet That other function being called from within, list_servers() was initially just trying to populate the values inside the global list variable itself, but was ending up in a similar fashion - reverting to initial empty value, but, the above now seems to work, as long as I first make reference to/manipulate/work with global variable instead of just trying to reassign it a brand new value/set of items? So, am I missing something obvious, have I forgotten about something else - yes, know that if was working from within an embedded function, I might need/want to then use the nonlocal statement against that variable name, but, honestly, just not sure how this can be occurring, and, it's not just with this one list variable, etc.? If I try simple test code from within the python interpreter, using different types of variables, this does also not seem to be the same all the time, but, don't think it can relate to an iterable like a list, or else, just in case, here is the code snippet with all the import statements from the top of that file, in case something could be overriding standard behaviour - not likely in this context, but, really not sure what's occurring: # import code snippet import requests, time from requests.auth import HTTPBasicAuth import psutil as psu import pytz import bcrypt from copy import copy from datetime import datetime, timedelta, timezone from dateutil.parser import parse # end of import snippet Thanks if you have any ideas/thoughts on the matter Jacob Kruger +2782 413 4791 "Resistance is futile!...Acceptance is versatile..." -- Regards, =dn -- ht
Re: Can one output something other than 'nan' for not a number values?
On 20/02/24 01:04, Chris Green via Python-list wrote:
dn wrote:
On 18/02/24 09:53, Grant Edwards via Python-list wrote:
On 2024-02-17, Cameron Simpson via Python-list wrote:
On 16Feb2024 22:12, Chris Green wrote:
I'm looking for a simple way to make NaN values output as something
like '-' or even just a space instead of the string 'nan'.
[...]
Battery Voltages and Currents
Leisure Battery - 12.42 volts -0.52 Amps
Starter Battery - nan voltsnan Amps
What I would like is for those 'nan' strings to be just a '-' or
something similar.
The simplest thing is probably just a function writing it how you want
it:
def float_s(f):
if isnan(f):
return "-"
return str(f)
and then use eg:
print(f'value is {float_s(value)}')
or whatever fits your code.
Except he's obviously using some sort of formatting to control the
number of columns and decimal places, so 'str(f)' is not going to cut
it. Is the basic floating point number formatting functionality seen
when using f-strings or '%' operator part of the float type or is it
part of the f-string and % operator?
It's part of the PSL's string library: "Format Specification
Mini-Language"
https://docs.python.org/3/library/string.html#format-specification-mini-language
Has the OP stated if we're talking 'Python' or numpy, pandas, ...?
Just python, on a Raspberry Pi, so currently Python 3.9.2.
Concur with earlier advice (and assuming is only a consideration during
output) - use if.
Alternately, encode appropriately during the data-capture phase.
--
Regards,
=dn
--
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Re: Can one output something other than 'nan' for not a number values?
On 20/02/24 05:58, Grant Edwards via Python-list wrote: Here's a demonstration of how to hook custom code into the f-string formatting engine. It's brilliantly depraved. https://stackoverflow.com/questions/55876683/hook-into-the-builtin-python-f-string-format-machinery From the above: You can, but only if you write evil code that probably should never end up in production software. So let's get started! I'm not going to integrate it into your library, but I will show you how to hook into the behavior of f-strings. This is roughly how it'll work: 1. Write a function that manipulates the bytecode instructions of code objects to replace FORMAT_VALUE instructions with calls to a hook function; 2. Customize the import mechanism to make sure that the bytecode of every module and package (except standard library modules and site-packages) is modified with that function. Final code is here: https://github.com/mivdnber/formathack Some of this (Expression components inside f-strings) newly available in v3.12 (PEP-701) - which can be used in production... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Testing (sorry)
On 19/02/24 12:09, Grant Edwards via Python-list wrote: ... But posts to the list still seemed to vanish into the ether while emails from both accounts reached other destinations without delay, During this process a number of posts from other users did appear in the list archive and at at _one_ of the two e-mail addresses which I had subscribed. But no sign of any of my posts. About 24 hours later, all of my posts (and the confirmation e-mails) all showed up in a burst at the same time on two different unrelated e-mail accounts. I still have no clue what was going on... Looking at the email-headers, there are sometimes considerable delays between messages submitted to the List-reflector, and their outward transmission (to me). Interestingly, there's something strange about the queuing. Instead of FIFO it seems some messages arrive ahead of others, ie out-of-sequence. (wonder if explained by submission via email or Usenet?) I've noted long delays too. Perhaps (also) to do with time-of-day? Always feel slightly embarrassed if 'repeat' an answer* that someone else had previously submitted, eg __new__ thread and @MRAB. However, if the reflector 'holds onto' the earlier message, then how should I/anyone know? * yes, repetition improves learning, slightly different words may help comprehension; but doubt I can express anything better than the aforementioned does/did/can. -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Can one output something other than 'nan' for not a number values?
On 18/02/24 09:53, Grant Edwards via Python-list wrote:
On 2024-02-17, Cameron Simpson via Python-list wrote:
On 16Feb2024 22:12, Chris Green wrote:
I'm looking for a simple way to make NaN values output as something
like '-' or even just a space instead of the string 'nan'.
[...]
Battery Voltages and Currents
Leisure Battery - 12.42 volts -0.52 Amps
Starter Battery - nan voltsnan Amps
What I would like is for those 'nan' strings to be just a '-' or
something similar.
The simplest thing is probably just a function writing it how you want
it:
def float_s(f):
if isnan(f):
return "-"
return str(f)
and then use eg:
print(f'value is {float_s(value)}')
or whatever fits your code.
Except he's obviously using some sort of formatting to control the
number of columns and decimal places, so 'str(f)' is not going to cut
it. Is the basic floating point number formatting functionality seen
when using f-strings or '%' operator part of the float type or is it
part of the f-string and % operator?
It's part of the PSL's string library: "Format Specification
Mini-Language"
https://docs.python.org/3/library/string.html#format-specification-mini-language
Has the OP stated if we're talking 'Python' or numpy, pandas, ...?
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: Using __new__
On 18/02/24 13:21, Jonathan Gossage wrote:
The problem is that if you are dealing with a library class, you may
have times when the superclass is 'object' while at other times, with a
different inheritance hierarchy, the superclass may need arguments. My
thought is that the object class __new__ method should not choke on
arguments, just ignore them.
All true.
So, what you're looking for is one mechanism to rule them all?
Not going to happen: for exactly the reasons you've stated. If you
really want to get right 'down into the weeds' with a __new__()
constructor, then you're well into customisation-territory.
I think it would be 'going nuts' but...
If it 'absolutely, positively, ...' then perhaps introspect the
super-class and modify the call based-upon whether it is 'something' or
"object"?
(in similar fashion to the singleton's if-statement attempting to make
sure it is unique)
- perhaps someone knows a better/proper way to do this?
Suggested research: custom classes, ABCs, and meta-classes...
See also recent improvements to Python which have made it easier for
sub-classes (and Descriptors - __set_name__() ) to identify
who/how/where to 'phone home', in case (also) applicable...
When I talk about 'object', I am talking about the ultimate base class
of any inheritance hierarchy. have seen the class named 'object' called
that.
Correct.
The earlier comment was that
class S( object ):
is 'tradition', and synonymous with:
class S:
(not disputing the concept of "object" as the base class)
Not correct.
Please see last paragraph from previous message:
On Sat, Feb 17, 2024 at 7:06 PM dn via Python-list
mailto:python-list@python.org>> wrote:
...
PS please reply to the list - there may be others who can learn
from, or
contribute to, this conversation!
...
--
Regards,
=dn
--
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Re: Using __new__
On 18/02/24 12:48, Jonathan Gossage wrote: The problem that I am facing is that when the superclass is not 'object', the __init__ method may well need arguments. I do not know how to determine if the superclass is 'object'. For what it is worth, any attempt to use this with different arguments should return the initial singleton and ignore further attempts to create a second instance. 1 "object" don't understand. Perhaps give us a broader description of the problem? Remember also ABCs (Abstract Base Classes). 2 arguments yes, must accommodate arguments in __new__() if some/same are needed in __init__() However, when using the default "object", the super() does not need, use, or want, any arguments to be passed. 3 singleton don't think that is happening! PS please reply to the list - there may be others who can learn from, or contribute to, this conversation! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Using __new__
On 18/02/24 11:35, Jonathan Gossage via Python-list wrote:
I am attempting to use the __new__ method in the following code:
class SingletonExample(object):
_instance = None
def __new__(cls, **kwargs):
if cls._instance is None:
cls._instance = super().__new__(cls, **kwargs)
return cls._instance
def __init__(self, **kwargs) -> None:
our_attributes = ('h', 'x')
if kwargs is not None:
for k, v in kwargs.items():
if k in our_attributes:
setattr(self, k, v)
a = SingletonExample(h=1)
and I get the following result:
(PRV) jonathan@jfgdev:/PR$ python -m Library.Testing.test2
Traceback (most recent call last):
File "", line 198, in _run_module_as_main
File "", line 88, in _run_code
File "/mnt/ProgrammingRenaissance/Library/Testing/test2.py", line 16, in
a = SingletonExample(h=1)
^
File "/mnt/ProgrammingRenaissance/Library/Testing/test2.py", line 6, in
__new__
cls._instance = super().__new__(cls, **kwargs)
^^
TypeError: object.__new__() takes exactly one argument (the type to
instantiate)
I am quite puzzled as it looks as if this code will not work if the
super-class is 'object'. Any suggestions on how to proceed?
Don't be puzzled. Read the error-message.
Change the super-call to: cls._instance = super().__new__(cls)
and happiness will follow...
That said, mystifications - not sure if this meets the/your definition*
of "singleton", because:
- it can be aliased, eg
a = SingletonExample(h=1)
b = SingletonExample(x=2)
- when it is, the effect is an accumulation of attributes and values
a = SingletonExample(h=1)
b = SingletonExample(h=2)
print( a.__dict__, b.__dict__, )
- it can be re-created with a different value, eg
a = SingletonExample(h=1)
a = SingletonExample(h=2)
- and can be 'regenerated':
a = SingletonExample(h=1)
a = SingletonExample(x=2)
- all failures are silent
* noting "Nowadays, the Singleton pattern has become so popular that
people may call something a singleton even if it solves just one of the
listed problems." (https://refactoring.guru/design-patterns/singleton)
YMMV!
--
Regards,
=dn
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Re: test-ignore
On 16/02/24 13:29, Skip Montanaro via Python-list wrote: Test post to see if my Newsgroup post program is working. Aim your test messages at alt.test, please. I agree that basic Usenet connectivity messages should go to alt.test. It's not clear from the original post, but if the poster's aim was to see if posts to comp.lang.python traverse the gateway and show up on this list, then alt.test won't help. Coincidentally (I hope), today have received a couple of poorly-executed spam/phishing messages purporting to be from this list or "Tutor". -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 4/02/24 13:20, avi.e.gr...@gmail.com wrote: Dave, You and I have had some experience in teaching or tutoring others and I think it fair to say our motivation is closer to teaching someone how they can fish for themselves rather than just handing them a fully-cooked fish. Which may push the debate 'up' a level, in that there are two pertinent Python Discussion Lists (amongst the many): Tutor which is expressly for learners (and tutors), and this one which is to discuss Python. Accordingly, one might suggest that people 'here' are looking for a direct answer - the fish (having tried to fish for themselves), but learners (seeking to learn to fish) should be asking elsewhere. This would sort-out the type/level of questions that OPs may have. As well as indicating an appropriate approach to 'answers'. However, there's no rule which says one has to ask in one place or the other (nor am I suggesting such, although...). Then again, might the lack of forethought evident in some questions and the forum-used, indicate a type of person who wouldn't investigate to see which is the best place for his/her enquiries anyway? Tutor List: https://mail.python.org/mailman/listinfo/tutor Lists Overview: https://mail.python.org/mailman/listinfo My favorite kinds of questions, thus, include someone who explains what they are trying to do and shows some code along with indications of what it produced (including error messages) and what it should produce. Then the question should not be a request to just FIX THIS or WRITE IT FOR ME but asking if someone can show what they did wrong with some idea where it went wrong. This may not be so common but it allows faster and easier help. +1 ... I will end with a comment. I have heard of interview techniques for a job where they deliberately supply a problem in which the goal is not so much to be easy to solve in front of them in real time but to watch how the person looking for a job responds to the uncertainties and asks follow-up questions or verbalizes things like, if it is like this, I might use this technique but if you also need that then ... So, I shudder to think what happens if someone being interviewed turns around and asks us and further confuses things with changes to make it harder to recognize they are asking for outside help. The answer expected may well be to NOT use say the older versions of PASCAL to do something but switch to something better suited (and for that matter available.) I would not want to program the DES encryption/decryption method in Pascal again! And these days, it seems much better to just find a module or package that meets such needs. As you know, I investigate Cognitive Psychology. Accordingly, such is interesting to me. In many cases, I'll interview for motivation, not just particular skills - but perhaps that's another can-of-worms. How about "when is 1 + 1 not 2?". This is a bit of a mind-bender, but leads towards debugging ability* - what if your code was showing some unbelievable result like this? The answer is (or rather, "could be") 10, ie we're looking at binary cf decimal, coding. Do I hear some groans? Yes, fair-enough! There was absolutely no "context" to the question - whereas when coding/debugging we would expect to have some 'framing' of our thinking. At the same time, 'fixed mode thinking' will prevent many people from even considering such possibilities - whether as-asked or in a dev.env... * In the ?good old days, career progression was thought to be: (mainframe) Computer Operator, to Computer Programmer, to Systems Analyst, etc. However, as I pointed-out (to an IBM 'big-wig' who took an instant dislike as a result) the valued skills of an Analyst are that (s)he can see 'patterns' - whereas the skills of debugging involve realising why an expected pattern doesn't work (as-expected). Another analysis might be to decide if the job requires a 'lateral thinker' or a more single-minded approach. (us lateral thinkers tend to ask (loads of) questions, and thus can be quite 'annoying' individuals). Then there is the main-stay of many job-adverts: "attention to detail" and the question of whether someone who can't [be bothered to] write an half-decent email-message (with spell-checker likely built-in) is going to be productive when communicating with a pedantic compiler? Again, some people are suited to this business (or specific jobs within), and some (?many) are not - but many are (perhaps reluctantly) programming to get some other job done... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
tion that goes something like "the poor will be with your always"? (?possibly Biblical) Whether we (here) are talking about 'poor' manners, 'poor' understanding, 'poor' communication skills, 'poor' Python knowledge, or whatever; isn't such one of the rationales for this DiscussionList? That said, we're all volunteering our (valuable) time! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
MTG: pytest (NZPUG, Auckland, VacExcHndlrs)
Wed 7 Feb (evening NZDT) will be the last virtual gathering in the
current Vacation Exception Handlers (VacExcHndlrs) series
(https://danceswithmice.info/Python/2024/VacExcHndlrs.html).
You are cordially-invited to join us to investigate the pytest Python
testing framework.
"The pytest framework makes it easy to write small, readable tests, and
can scale to support complex functional testing for applications and
libraries."
Pre-requisites:
1 Head-set to ask questions and make contributions
2 Lab-/Log-/Note-book
3 Python 3.8+ installed
4 Ability to write intro-level Python program[me]s (at least)
5 Credentials to install from PyPi ("The Cheese Shop")
6 Preparedness to research, experiment, work with others...
As before, we will follow a café style of meeting. So, come prepared
with a list of objectives you would like to achieve and a list of
achievements you will be ready to share.
Possible (but far too many) topics:
- installing pytest (individual, system-wide, PyCharm, VSCodium, ...)
- TDD's (Test-Driven Development) red-green refactoring
- the Python assert-statement
- the project directory-tree and auto-discovery
- adding simple-tests
- running pytest
- reporting
- structuring the code-base to facilitate testing
- advantages/disadvantages of automated testing
- using a GAI to suggest/generate tests
- fixtures and dependencies (set-up and/or tear-down)
- scopes (function, class, module, session)
- parametrizing
- monkey-patching
- CI/CD chaining you've built
- plug-ins you're finding helpful
- coverage
- testing strategies
- other testing frameworks and aids
(open-ended - what would you like to add?)
Come to participate, learn-from, and help others!
Please RSVP at https://www.meetup.com/nzpug-auckland/events/298901851/
--
Regards,
=dn
--
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Re: Extract lines from file, add to new files
On 30/01/24 05:15, Rich Shepard via Python-list wrote: On Fri, 12 Jan 2024, Rich Shepard via Python-list wrote: For my use 1) the salutation and email address (always with an '@') are sequential and 2) I'm developing the script to extract both from the same file. I've looked at my Python books "Python Crash Course," "Effective Python," and "Python Tricks The Book" as well as web pages in my searches without finding the answer to what may be a simple question: how to specify a variable in one file that has its values in another file. Specifically, how to I designate the salutation holder in the message file and pass it the name value from the name/email address file? If this explanation is not sufficiently clear I'll re-write it. :-) It seems clear - but maybe we (all) misunderstand? The books don't cover it - but is there a reason why they don't? (Thunderbird did not thread this message with earlier ones, and it seems some time has passed/memory is fading - but hopefully have remembered content) As said previously, the idea of two physical-files containing logically-related data (without any form of cross-reference between) is bad design. In the current file, there is one physical structure and each person's details are logically-related by proximity. A long way from ideal, but workable (as you've described). However, once split into two files, there is no way to guarantee that the two logically-related data-items (name and address) will continue to be related by their physical position in the respective files. Worse: whilst it would seem apparent that "Alice" from the names file might be related to the address "al...@domain.tld", how could one know if "Bob" actually corresponds to "list-mem...@domain.tld"? This is why dicts, databases, etc, offer keys (as labels for data-items/dependent components)! After a quick look at Eric's Crash Course, yes, his files-intro example (digits of pi) is unlikely to have any practical reality (and I work with statisticians and quants!). However, at the end of that chapter (10), there is mention of JSON files. A JSON version of the existing single-file structure will provide human-readable labeling of data-items, give better separation between individuals' data, and show how name and address are linked. Recommend solving 'the problem' that way! (as previously discussed by others 'here', IIRC) Slatkin's Effective Python doesn't seem to discuss the basics of files at all (presumes such knowledge of the reader). It dives into important, but rather technical discussions, comparing strings and bytes - somewhat beyond the complexity-level of this discussion. That book does however include discussions such as "Prefer Multiple Assignment Unpacking over Indexing" (Item 6 - also points to Item 19) where relative-positioning (indexing in other words) is advised-against. If you wish to persist with this two-file structure, please see earlier responses (again, IIRC) and discussion of file-merge operations. As these date back to mainframes and the days of storing files on mag-tape, I'd be surprised to see them discussed in 'modern' texts. However, the principle is: read a record from each file, do-the-business, read the next 'pair' of physically-related records, rinse-and-repeat. If you require further assistance: how about showing a couple of relevant lines of the data-file(s) and the pertinent parts of the code, along with a description of what's going-wrong or not making sense to you? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 15/01/24 21:13, Greg Ewing via Python-list wrote: On 15/01/24 1:54 pm, dn wrote: Soon after, Wirth simplified rather than expanded, and developed Pascal. Before Pascal there was Algol-W, which Wirth invented as a rebellion against how complicated Algol 68 was becoming. When I first saw this I was stunned, then attracted to its simplicity, but then steered-away once realised that it needed 'more' to cope with 'the outside world'. Pascal was intended as a teaching language, and as such it was lacking in practicality in a few spots. But it didn't need much tweaking to make it a very useful language. UCSD Pascal, Turbo Pascal, Delphi, etc. enjoyed a lot of popularity. A variant of UCSD was the main language for Macintosh application development for a number of years. Ironically, I didn't come across Pascal as a teaching-language. Borland were trying to turn Turbo Pascal into a practical development environment, beyond teaching (as with others of their 'Turbo' series). As I say, it didn't float my business-world boat. - not before I won a case a wine from Philippe Kahn's own vineyard for solving some 'interview question' and exchanging jokes with him, in French, at some Trade Show in London. Two surprises: one, that it actually turned-up a few weeks later, and two, that I (suddenly) had so many friends! Ah, the good, old days... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 15/01/24 14:45, Chris Angelico wrote: On Mon, 15 Jan 2024 at 12:42, dn via Python-list wrote: On 15/01/24 14:33, Chris Angelico via Python-list wrote: On Mon, 15 Jan 2024 at 12:12, dn via Python-list wrote: Here's another witticism I'll often toss at trainees (in many languages, and especially in UX): just because we can do it, doesn't make it a good idea! Programming. We were so busy with whether we COULD that we didn't stop to think if we SHOULD. I think that's basically my whole life. Don't be too hard on yourself. My life-advice has always been "don't do anything I wouldn't do" - which pretty-much gives you carte blanche. I would NEVER give that advice to anyone. They would leave the dishes unwashed, and a number of other problems :) I'd soon have you sorted-out - except for one small problem: all the dishes have been done! If you can get here before the rain, the lawn needs mowing... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 15/01/24 14:33, Chris Angelico via Python-list wrote: On Mon, 15 Jan 2024 at 12:12, dn via Python-list wrote: Here's another witticism I'll often toss at trainees (in many languages, and especially in UX): just because we can do it, doesn't make it a good idea! Programming. We were so busy with whether we COULD that we didn't stop to think if we SHOULD. I think that's basically my whole life. Don't be too hard on yourself. My life-advice has always been "don't do anything I wouldn't do" - which pretty-much gives you carte blanche. -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 15/01/24 11:47, Chris Angelico via Python-list wrote: On Mon, 15 Jan 2024 at 09:40, dn via Python-list wrote: The basic challenge came from my earlier (and blasé) repetition of the Python refrain "everything in Python is an object". Which led to: ... So, no, there's an "everything" which (might be) an object but which cannot be used in that scenario. More accurately, every VALUE in Python is an object. This does not mean that syntax is an object. Very few languages would say that every single grammatical element is a value. +1 Thank you. This old-dog will try to re-learn that term... Yes, it's sloppy to say "everything" is an object, but it's also rather nonintuitive to claim that, therefore, syntax elements are all objects. It's like claiming that everything that this dealership sells is a car (or "everything in this dealership is a car"), and therefore the dealership's name must itself be a car. To say nothing of 'extended warranties'! (and their dubious rationale) That said, does anyone think that something like: for a_function( etc ) in iterable/iterator: is acceptable? - see both Python definition and (full-)quotation. I've not come-across a language which does allow such - YMMV/mea culpa; and am struggling to see how it could possibly be useful. You could do something close to that: for a_function(etc)[0] in iterable: ... because an assignment target can contain an arbitrary expression followed by the subscript. Here's another witticism I'll often toss at trainees (in many languages, and especially in UX): just because we can do it, doesn't make it a good idea! * Looking at the correspondent's email-address (cf 'handle') - and as an unfair stereotype, raises the question of issues related to (English) language-skills - which, arrogantly implies/assumes that native English-speakers are all highly-capable. (?) A negative-interpretation is to note his apparent intelligence, but wonder if failing to represent others' comments fairly is deliberate, or carelessness. Is there an irony in behaving/failing in such, whilst attempting to hold Python's structure to some golden-ideal? Seems likely. -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 15/01/24 08:06, AVI GROSS via Python-list wrote: ...> You provided a way to create an anonymous function and that was not enough. I wonder if you could throw in the new := walrus operator to similarly make a named lambda function in a similar way. Why would @Chris have anything to do with the 'walrus-operator'? PS our interlocutor doesn't like colloquialisms such as these - despite them being near-and-dear to our hearts! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
t; but acted similar to one.
I believe "module" objects were among the last to transition into
object inheritance lane, which might have happened some time around
Python 3.5. Of course, there are plenty of things that are "in
Python", at least due to its grammar, that are hard to describe as
objects (eg. comments). So, you'd have to make a special subset of
Python language that (eg. excludes comments) to claim that everything
is an object.
Most importantly, however, regardless of what you understand to be an
object, or how you decide to answer any of those questions: what value
does such a claim possibly have? Especially, given the context...
Intriguing. I laughed when I first saw Python's docstrings (one type of
"comment") because it was obvious (to me) that they were being treated
as strings. The fact that they were not identified ("assigned" or
"bound", if you prefer) is neither here-nor-there.
(just as, on the RHS, all Python-functions return a value, even if it is
None - which is not obvious to many, at-first)
Admittedly, a #-comment does not qualify as an object; but then the hash
is an exclusion signal, which the lexer understands as ending the
logical line.
Thus, a comment has meaning at 'compile time', but not at 'execution
time'. Such would be true, strictly-speaking. However, most of us would
say that a comment 'has no meaning' in terms of the parser, and what it
delivers.
Shall we change the phrase to "everything in Python, at run-time, is an
object"? As a phrase it is obiter-dictum, not ratio decidendi! (to use a
language which has only extended in dubious modes for the last
couple-of-thousand years - but which still has illogical structure)
Suspect that clumsy exclusion also lacks precision to the standard being
demanded. Thus return to the suggestion that you seem in the wrong
place, because Python doesn't meet the required standard. Sorry!
--
Regards,
=dn
--
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Re: Extract lines from file, add to new files
On 15/01/24 10:23, Chris Angelico via Python-list wrote: On Mon, 15 Jan 2024 at 08:15, Left Right wrote: Python grammar rules prevent function definition from appearing in left-hand side of the head of the for loop. However, a variable declaration, which is also a statement, is allowed there. What is a "variable declaration" in Python? Please elaborate. We may be in danger of disappearing down an unintended 'rabbit hole' with this side-discussion (he says, with graceful under-statement). The basic challenge came from my earlier (and blasé) repetition of the Python refrain "everything in Python is an object". Which led to: <<< For example, you may say "functions in Python are objects", but you cannot put a function definition in the head of the for loop clause. >>> Which is logical - to some degree, and in-isolation. for def a_function( etc )... in iterable/iterator: does not make sense. The 'head' (a more generic name, where Python says "target_list", that refines down to 'something which can identify the generated-value'. So, no, there's an "everything" which (might be) an object but which cannot be used in that scenario. Two "howevers": However, instead of looking at the narrow clause, (third comment about wording not being taken as an whole!!!)* the full quotation was: <<< In Python, everything is an object. As long as the LHS is a legal-object which makes sense for the situation, it can be used. >>> Context! However, from the docs: "A function definition defines a user-defined function object (see section The standard type hierarchy)". Accordingly, is a function-definition an object? No! It defines an object. That said, does anyone think that something like: for a_function( etc ) in iterable/iterator: is acceptable? - see both Python definition and (full-)quotation. I've not come-across a language which does allow such - YMMV/mea culpa; and am struggling to see how it could possibly be useful. In-turn, how this discussion could become profitable... * Looking at the correspondent's email-address (cf 'handle') - and as an unfair stereotype, raises the question of issues related to (English) language-skills - which, arrogantly implies/assumes that native English-speakers are all highly-capable. (?) A negative-interpretation is to note his apparent intelligence, but wonder if failing to represent others' comments fairly is deliberate, or carelessness. Is there an irony in behaving/failing in such, whilst attempting to hold Python's structure to some golden-ideal? Web.Refs: https://docs.python.org/3/reference/compound_stmts.html#the-for-statement https://docs.python.org/3/reference/simple_stmts.html#grammar-token-python-grammar-target_list https://docs.python.org/3/reference/compound_stmts.html#function-definitions -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 14/01/24 16:48, Chris Angelico wrote: On Sun, 14 Jan 2024 at 14:43, dn via Python-list wrote: Similarly, whilst we could write: a, b, c = 1, 2, 3 I would only do this when it aligns particularly well with the algorithm being implemented. For example, you could start a Fibonacci evaluator with "a, b = 0, 1". Otherwise, there's not all that much reason to unpack three constants in this way. (Though I am much more likely to use multiple initialization to set a bunch of things to the SAME value, lilke "a = b = c = 0".) Neatly stated! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
tant to remember. If someone calls you
"mate", that has different connotations depending upon whether you're
friends, you're on a Navy ship, or in a more intimate situation - indeed
there are some cultures in which the word "mate" is not used to mean
'friend' at all. Which is (more) right? Which wrong?
Perhaps you're aiming for, or even used to, a more perfect and
predictable language?
Anyways. To the OP: I'm sorry to hijack your question. Below is the
complete program:
with (
open('example.txt', 'r') as e,
open('emails.txt', 'w') as m,
open('salutations.txt', 'w') as s,
):
for line in e:
if line.strip():
(m if '@' in line else s).write(line)
Please see responses elsewhere which say why this sort of thing, whilst
possible and 'easy', is not recommendable.
it turned out to be not quite the golfing material I was hoping for.
But, perhaps a somewhat interesting aspect of this program you don't
see used a lot in the wild is the parenthesis in the "with" head. So,
it's not a total write-off from the learning perspective. I.e. w/o
looking at the grammar, and had I have this code in a coding interview
question, I wouldn't be quite sure whether this code would work or
not: one way to interpret what's going on here is to think that the
expression inside parentheses is a tuple, and since tuples aren't
context managers, it wouldn't have worked (or maybe not even parsed as
"as" wouldn't be allowed inside tuple definition since there's no
"universal as-expression" in Python it's hard to tell what the rules
are). But, it turns out there's a form of "with" that has parentheses
for decoration purposes, and that's why it parses and works to the
desired effect.
Again, context! All that is important 'here' is how to 'link' the
file-descriptor with an identifier. Similarly, whilst we could write:
a, b, c = 1, 2, 3
(and BTW that is legal Python - for anyone seeing such for the first time)
and whilst it is shorter (and I've been known to write such), the need
to read carefully in order to pair-up the relative positions make it
less readable than
a = 1; b = 2; c = 3
(and some would argue, quite reasonably, that it would be better were
they on separate lines)
Similarly, many dev.teams have a 'standard' which suggests that once a
function/method has three or more arguments, relative-positioning should
go out-the-window, in favor of named-arguments. This speeds
comprehension and reduces errors.
In the original mental-model, the difficulty was which file-descriptor
would be paired with which file (previously described). The multiple
as-s make it more readable and more comprehensible.
Since it looks like you are doing this for educational reasons, I
think there's a tiny bit of value to my effort.
That's what we're (all) here for!
(and not forgetting that the OP described a skill-level well below that
of most of this post and your question, which enabled (and deserved,
IMHO) appropriate respect).
--
Regards,
=dn
--
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Mtg: Object-Oriented VacExcHndlrs (UTC+13)
Let's meet on Wednesday (17Jan, 1600 NZDT (UTC+13), wearing a head-set) to talk about Object-Oriented everything. Is O-O worthwhile, or does is it just a load of guys running around and getting no-where? NB this is not a formal PUG-meeting. It's part of the "Vacation Exception Handlers" series (https://danceswithmice.info/Python/2024/VacExcHndlrs.html) - virtual-gatherings for folk left-behind to keep the wheels turning, whilst everyone else swans-off sunning themselves... (non-Kiwis please remember: it's not just school vacation, but summer-time down-under. Wish you were here?) Café-style approach, so there will be no formal presentation. All welcome. No presumption of knowledge/skill. This gathering is for everyone, from Beginner to Python-Master. Is Python an Object-Oriented language? Why does Python use (what appear to be) procedural constructs for so many of its core functions, eg len(a_list) rather than a_list.length() and sqrt(a_number) rather than a_number.sqrt()? Why do pythonista say "everything in Python is an object"? Is it faster to write in an OOP-style and/or does OOP-code run faster? If not, why bother? - insert your question here: What do you want to know? What has been bothering you about OOP (or O-O in Python) that you'd like to settle? To join us (we don't bite!), please RSVP at https://www.meetup.com/nzpug-auckland/events/298536620/ -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 12/01/24 08:53, Rich Shepard via Python-list wrote:
On Thu, 11 Jan 2024, Piergiorgio Sartor via Python-list wrote:
Why not to use bash script for all?
Piergiorgio,
That's certainly a possibility, and may well be better than python for this
task.
(sitting in a meeting with little to occupy my mind, whilst tidying
email-InBox came back to this conversation)
In the bare-description of the task, I might agree to sticking with
BASH. The OP did say that the output from this will become input to a
sed/mailx task!
(we trust, does not involve spamming innocent folk)
However, that task could also be accomplished in Python. So, unless
there is an existing script (perhaps) quite why one would choose to do
half in Python and half in BASH (or...) is a question.
Because this is a Python forum, do the whole thing in one mode - our mode!
Previous suggestions involved identifying a line by its content.
Could use a neat state-transition solution.
However, there is no need to consider the input-data as lines because of
the concept of "white-space", well-utilised by some of Python's built-in
string-functions. See code-sample, below.
As mentioned before, the idea of splitting the one file (data-items
related by serial-progression) and creating two quite-separate
data-constructs (in this case: one holding the person's name in one file
and the other the person's email-address in another) which are related
'across', ie line-by-line, is an architectural error?horror. Such would
be hard to maintain, and over-time impossible to guarantee integrity.
Assuming this is not a one-off exercise, see elsewhere for advice to
store the captured data in some more-useful format, eg JSON, CSV, or
even put into a MongoDB or RDBMS.
** code
""" PythonExperiments:rich.py
Demonstrate string extraction.
"""
__author__ = "dn, IT&T Consultant"
__python__ = "3.12"
__created__ = "PyCharm, 14 Jan 2024"
__copyright__ = "Copyright © 2024~"
__license__ = "GNU General Public License v3.0"
# PSL
import more_itertools as it
DATA_FILE = "rich_data_file"
READ_ONLY = "r"
AS_PAIRS = 2
STRICT_PAIRING = True
if __name__ == "__main__":
print("\nCommencing execution\n")
with open( DATA_FILE, READ_ONLY, ) as df:
data = df.read()
data_as_list = data.split()
paired_data = it.chunked( data_as_list, AS_PAIRS, STRICT_PAIRING, )
for name, email_address in paired_data:
# replace this with email-function
# and/or with storage-function
print( name, email_address, )
print("\nTerminating")
** sample output
Calvin cal...@example.com
Hobbs ho...@some.com
...
**
--
Regards,
=dn
--
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Re: Extract lines from file, add to new files
On 12/01/24 12:56, Chris Angelico via Python-list wrote: On Fri, 12 Jan 2024 at 08:56, Left Right via Python-list wrote: By the way, in an attempt to golf this problem, I discovered this, which seems like a parser problem: When you jump immediately to "this is a bug", all you do is make "seems"! but yes, it is a (much) less-likely explanation. yourself look like an idiot. Unsurprisingly, this is NOT a bug, this is simply that you didn't understand what was going on. The grammar isn't easy to read, and it's usually better to read the documentation instead. Those of us who studied Computer Science may well have been taught/expected to learn how to read [modified] BNF - indeed to have worked in that (cf coding in Python). Accordingly, the English text is likely easier to understand, but sometimes the BNF offers finer-detail or can be used to clarify some mis- or insufficiently-understood aspect of the text. IMHO/YMMV/etc... (Plus, golfing isn't really a goal in Python, and you didn't shorten the code by much at all. Good job.) I took my hat off to the poster, being prepared to dive-in and do this. Accordingly, was more than happy to help set him/her back onto 'the straight and narrow'. (yes it was a BNF-failing - which, credit where credit's due, I think was realised at the same time as response was typed) How many others just want us to do all their thinking for them? (there's a rude comment about wiping noses - but probably a step too far wrt the CoC) -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Extract lines from file, add to new files
On 12/01/24 10:33, Left Right via Python-list wrote:
By the way, in an attempt to golf this problem, I discovered this,
which seems like a parser problem:
This is what Python tells me about its grammar:
with_stmt:
| 'with' '(' ','.with_item+ ','? ')' ':' block
| 'with' ','.with_item+ ':' [TYPE_COMMENT] block
| ASYNC 'with' '(' ','.with_item+ ','? ')' ':' block
| ASYNC 'with' ','.with_item+ ':' [TYPE_COMMENT] block
with_item:
| expression 'as' star_target &(',' | ')' | ':')
| expression
From which I figured why not something like this:
with (open('example.txt', 'r'), open('emails.txt', 'w'),
open('salutations.txt', 'w')) as e, m, s:
for line in e:
if line.strip():
(m if '@' in line else s).write(line)
Which, surprise, parsers! But it seems like it's parse is wrong,
because running this I get:
❯ python ./split_emails.py
Traceback (most recent call last):
File "/home/?/doodles/python/./split_emails.py", line 1, in
with (open('example.txt', 'r'), open('emails.txt', 'w'),
open('salutations.txt', 'w')) as e, m, s:
TypeError: 'tuple' object does not support the context manager protocol
It seems to me it shouldn't have been parsed as a tuple. The
parenthesis should've been interpreted just as a decoration.
NB. I'm using 3.11.6.
A series of comma-separated items will be parsed as a tuple (some people
think it is bounding-parentheses which define).
In this case, the issue is 'connecting' the context-manager "expression"
with its (as) "target". These should be more-closely paired:-
with ( open( 'example.txt', 'r', ) as e,
open( 'emails.txt', 'w', ) as m,
open( 'salutations.txt', 'w', ) as s
):
(NB code not executed here)
A data-architecture of having related-data in separated serial-files is
NOT recommendable!
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: A problem with str VS int.
On 12/12/23 21:22, Steve GS wrote: With all these suggestions on how to fix it, no one seems to answer why it fails only when entering a two-digit number. One and three work fine when comparing with str values. It is interesting that the leading 0 on a two digit worked. Still, one digit and three digit work but not two. This is now more of a curiosity as I did use the integer comparisons. Emphasis on the word "seems"! Did you try running the code provided earlier? Did you notice that such illustrated what happens when using strings which appear as numbers, and showed how a three digit number (expressed as a string) may well precede a two- (or even a one-) digit number in the same form - and that the end-result of the sequence of integers is quite-different to the sequence of integer-values expressed as strings! Why does this happen? Because of the way data is encoded. It is language independent. The definition of order or sequence is called "collation". "Comparisons" establish relative-sequence. You will find some handy explanations of how comparisons work (eg equals or less-than) in the Python manual. After working through those three steps, if there's something that's still mystifying, please refine the question... Web.Refs: https://en.wikipedia.org/wiki/Collation https://docs.python.org/3/reference/expressions.html?highlight=comparison#value-comparisons https://docs.python.org/3/howto/sorting.html?highlight=sort -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: A problem with str VS int.
On 10/12/23 15:42, Steve GS via Python-list wrote:
If I enter a one-digit input or a three-digit number, the code works but if I
enter a two digit number, the if statement fails and the else condition
prevails.
tsReading = input(" Enter the " + Brand + " test strip reading: ")
if tsReading == "": tsReading = "0"
print(tsReading)
if ((tsReading < "400") and (tsReading >= "0")):
tsDose = GetDose(sReading)
print(tsReading + "-" + tsDose)
ValueFailed = False
else:
print("Enter valid sensor test strip Reading.")
I converted the variable to int along with the if statement comparison and it
works as expected.
See if it fails for you...
It works as expected (by Python)! This is how strings are compared -
which is not the same as the apparently-equivalent numeric comparison.
Think about what you expect from the code below, and then take it for a
spin (of mental agility):
values = [ 333, 33, 3, 222, 22, 2, 111, 11, 1, ]
print( sorted( values ) )
strings = [ "333", "33", "3", "222", "22", "2", "111", "11", "1", ]
print( sorted( strings ) )
The application's data appears numeric (GetDose() decides!).
Accordingly, treat it so by wrapping int() or float() within a
try-except (and adjusting thereafter...).
"But wait, there's more!"
(assuming implement as-above):
if 0 <= ts_reading < 400:
1 consistent 'direction' of the comparisons = readability
2 able to "chain" the comparisons = convenience
3 identifier is PEP-008-compliant = quality and style
--
Regards,
=dn
--
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Re: How/where to store calibration values - written by program A, read by program B
On 7/12/23 07:12, MRAB via Python-list wrote:
On 2023-12-06 12:23, Thomas Passin via Python-list wrote:
On 12/6/2023 6:35 AM, Barry Scott via Python-list wrote:
On 6 Dec 2023, at 09:32, Chris Green via Python-list
wrote:
My requirement is *slightly* more complex than just key value pairs,
it has one level of hierarchy, e.g.:-
KEY1:
a: v1
c: v3
d: v4
KEY2:
a: v7
b: v5
d: v6
Different numbers of value pairs under each KEY.
JSON will allow you to nest dictionaries.
{
'KEY1': {
'a': v1
'c': v3
'd': v4
}
'KEY2': {
'a': v7
'b': v5
'd': v6
}
}
Personally I would not use .ini style these days as the format does
not include type of the data.
Neither does JSON. Besides, JSON is more complicated than necessary
here - in fact, your example isn't even legal JSON since lines are
missing commas.
Fun fact - for at least some, maybe most, JSON files, using eval() on
them is hugely faster than using Python's standard JSON library. I
learned this when I wanted to ingest a large browser bookmarks JSON
file. It wouldn't matter for a much smaller file, of course.
It would be safer if you used literal_eval.
Ah, memories of Python2...
Does this little hack still work?
What about True/False cf true/false?
--
Regards,
=dn
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NZPUG Mtg: Making Python faster, and "Dependency Inversion"
Virtual meeting: Wednesday 6 December, 1815 for 1830 NZDT/UTC+13 Book at https://www.meetup.com/nzpug-auckland/events/295433876/ 1 Making Python faster - using type hints Tushar will lead us through: A brief history of type hints Using type checkers to verify your type hints Compiling type checked Python to make it faster Some examples of libraries and the speedups they get from type hints We'll be looking at mypy/mypyc. Audience Level: intermediate, ie understand Python constructs, functions, control flow, etc. Tushar has been a long term Python developer, OSS contributor, author and speaker. He has been working with static analysis and type checkers for the past 3 years, and has contributed to various PSF-projects such as black and mypy. 2 SOLID's Dependency Inversion Principle Olaf will complete the current Software Craftsmanship series on the SOLID Principles with a session on the Dependency Inversion Principle. This one is particularly fascinating, because at first-glance the inversion seems to be asking us to do things backwards. With understanding, we realise that it is an impressive device enabling us to focus on what is needed by the 'layer' of more valuable components, rather than the lower-level, eg UIs and external interfaces (need refresher? see https://www.bmc.com/blogs/solid-design-principles/) Audience Level: advanced, ie understand programming constructs, patterns, principles, etc. Olaf needs no introduction having generously brought us the earlier sessions in his "Software Craftsmanship" series over the last two years. Let's complete this exercise in dogged-persistence and round things off neatly - if you remember, this talk was originally scheduled last month, but technical-gremlins got in the way! Also, please tell us what topics you'd like to cover at this skill-level in future... Please come, and come with a collegial frame-of-mind. Questions and conversation will be the order of the day. If you are more confident in Python, your constructive advice, suggestions, and alternate approaches will be valued ... -- Regards =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Newline (NuBe Question)
On 15/11/2023 20.25, Grizzy Adams via Python-list wrote:
Hi & thanks for patience with what could be simple to you
Have this (from an online "classes" tutorial)
There are lots of on-line classes!
--- Start Code Snippit ---
students = []
grades = []
for s in geographyClass:
students.append(geographyStudent(s))
for s in students:
grades.append(s.school)
grades.append(s.name)
grades.append(s.finalGrade())
if s.finalGrade()>82:
grades.append("Pass")
else:
grades.append("Fail")
print(grades)
--- End Code Snippit ---
I have extended (from tutorial) it a bit, I would really like to have a newline
at end of each record, I have searched (and tested) but cant get "\n" to give a
newline, I get "Mydata\n"
Do I need to replace "append" with "print", or is there a way to get the
newline in as I append to list?
Don't know how "Mydata..." results - where is it in the code.
What do you see when grades is printed?
Do you really want data-values all mashed together?
Yes, what changed after removal of all the .append()-s, and instead,
within the (second) for-loop print( school, name, ... ) was used?
Is it easier to go on from there?
--
Regards,
=dn
--
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Clearing the Deque • Picturing Python’s `deque` data structure
You will be welcome to join us at our next (hybrid) meeting: Wednesday, 15 November 2023, 1815~2030 NZDT (0515~0730 UTC). How often do you use a deque*? “Not very” is a common answer. Perhaps you’ve never used it. In this presentation, Stephen won’t try to convince you to use it more often. Instead, he’ll present a different perspective on what this data structure is, and how it differs from a list. The presentation will compare deques and lists in a visual manner, to help us understand why we may need a deque in certain situations. We’ll also explore some demonstration examples to highlight the differences in performance between the two data structures in different scenarios. *pronounced like “deck" Audience: This presentation is ideal for those who have either never heard of deque, or have heard of it but never really used it or understood why it’s needed. The more experienced may find the visual story insightful. Stephen used to be a physicist, which is where he learned programming. After working in science and academia for over a decade, he decided to escape before it was too late. Since then, has focused exclusively on teaching coding and communicating about Python. A big part of his day is busy with running Codetoday—we teach Python coding to children between 7 and 16 years old (https://www.codetoday.co.uk/). He also runs courses for adults and corporate training programs, and particularly, writing about Python. He writes the articles he wished he had when learning. He publishes articles at The Python Coding Stack (https://thepythoncodingstack.substack.com/) and also wrote an online book (soon to be in other formats, too) for beginners, The Python Coding Book (https://thepythoncodingbook.com/). Please RSVP on Meetup.com (NZPUG Auckland Branch): https://www.meetup.com/nzpug-auckland/events/295433874/ -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: fCONV_AUSRICHTG is not defined - Why?
On 08/11/2023 06.47, Egon Frerich via Python-list wrote: I've no idea why this happens. In a module there are lists and definitions: ... ["%s%s%s " % (i[fCONV_AUSRICHTG], i[fLG2], i[fTYP]) for i in Felder]) File "/home/egon/Entw/Geldspur/geldspur/gui/GUI_Konfig.py", line 90, in ["%s%s%s " % (i[fCONV_AUSRICHTG], i[fLG2], i[fTYP]) for i in Felder]) NameError: name 'fCONV_AUSRICHTG' is not defined You see "Felder" and with "0 0 3 4" the correct value 4 for fCONV_AUSRICHTG. But there is the NameError. What does mean? Is there a change from python2 to python3? Works for me (Python 3.11 on Fedora-Linux 37) - both as a script, and simple/single import. What happens when you extract the second dimension's definitions into a module of their own, and import that (with/out less-sophisticated join)? -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Safe package removal
After thread: "pip/pip3 confusion and keeping up to date" Over the years?centuries, have added various packages, using all of: - distribution-installer (dnf/yum - per apt-get) - su pip install, and - (user) pip install Because Fedora-Linux can be upgraded in-place. an amount of 'crud' hangs-about 'forever'. Accordingly, python -m pip list --outdated shows about as many entries as python - m pip list! Have (comparatively recently) standardised that projects not inside a VM or Container, will be managed by Poetry. (It's working well!) Q1 Can all (user) pip installs be safely removed, 'just like that'? Q2 How can one ascertain if system (su/sudo) pip installed packages can be removed - or are used by the op-sys/some important application? Q3 Similarly, if one can uninstall those originally installed using the distribution-installer, or if something, somewhere, will 'break'? (yes, there's an upgrade to Fedora 38 in "The Backlog") -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Checking if email is valid
On 02/11/2023 20.28, Simon Connah wrote: I'm not sure that would be practical. As I'm setting up a mailing list server I don't know if someone in the future is going to need to use one of those aliases and testing manually would be tedious. Please re-read. Discussion is about "closeness". Thus, what you might expect from email servers and Admins, NOT what you should do. That part should be quite evident by now! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Checking if email is valid
On 02/11/2023 19.56, Chris Angelico via Python-list wrote: On Thu, 2 Nov 2023 at 17:47, Simon Connah wrote: My goal is to make a simple mailing list platform. I guess I could just send email to an address and if it bounces then I can remove it from the database. Thing is I'm not sure how close to a real email address an email has to be in order to be bounced. If it was completely wrong it might just swallowed up. Every address is completely separate. There is no "closeness". Just send email to an address. Agreed. However, with names that are frequently misspelled or which are commonly-spelled slightly differently, the 'trick' is to anticipate problems and set up aliases which forward messages to the correct address*. eg Kelvin -> Kevlin Niel, Neal, Neale (etc) -> Neil (in the same way that GoodLookingGuy@mydomain -> me, or (more likely) MailAdmin -> me) * however, this can end-up perpetuating the mistake, rather than correcting... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Checking if email is valid
On 02/11/2023 19.46, Simon Connah via Python-list wrote: On Thu, 2 Nov 2023 at 05:21, Simon Connah via Python-list python-list@python.org wrote: Could someone push me in the right direction please? I just want to find out if a string is a valid email address. There is only one way to know that a string is a valid email address, and that's to send an email to it. What is your goal though? For example, if you're trying to autolink email addresses in text, you don't really care whether it's valid, only that it looks like an address. My goal is to make a simple mailing list platform. I guess I could just send email to an address and if it bounces then I can remove it from the database. Thing is I'm not sure how close to a real email address an email has to be in order to be bounced. If it was completely wrong it might just swallowed up. Exactly! Build a complementary script which inspects the returned/bounced messages, and removes those addresses. Given that the list of addresses is built from people signing-up in the first place, one has to presume that people know their own addresses and can type - there's no real defence against 'stupid'*. It's not as if you are making-up addresses yourself (in many jurisdictions it is illegal without opt-in). An email address: account@domain, has to be accurate in two ways: 1 the domain - otherwise the DNS (Domain Name System) won't be able to locate the destination email server 2 the account - otherwise the email server won't know to which mail-box the message should be delivered. The (1) is why there was some suggestion of using MX records (but may as well just send the message). The problem with (2) is that some servers will 'bounce' a message, but others will let it die silently (not wanting to add to email-spam by sending stuff 'back' if the message was spam in the first place!) The exception to (2) is a "catch-all" address, which accepts every message not addressed to a (legal) mail-box. These are sometimes used to deal with messages addressed to a staff-member who has left (for example). However, are somewhat problematic because they pick-up tons of garbage (eg earlier today I received a message to 456...@domain.tld. This is not, and never has been, a mail-box on the domain; but would drop into a catch-all mail-box. It would be an unusual MailAdmin inspecting a catch-all address, who would return a mis-addressed email to its source. If the message was addressed to s...@domain.tld, I'd be more likely to assume it was for you, and forward it to you (in the expectation that you'd fix the problem with the sender...). However, ... There are some large businesses doing what you've outlined. They have not solved this problem - and not through lack of trying! * as fast as you make something idiot-proof, the world will show you an 'improved' class of idiot! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Checking if email is valid
On 02/11/2023 00.35, Simon Connah via Python-list wrote: OK. I've been doing some reading and that you should avoid regex to check email addresses. This operation used to be a BIG THING back in the days of 'everyone' building PHP web-sites. When there were only a handful of TLDs (top-level domain names, eg the country-codes* such as .nz and .uk plus the generics such as .com and .net. Accordingly, one could hold the entire list for convenience of checking. However when IANA (the outfit responsible for the Root Zone Database and especially ICANN realised that there was money to be made, they allowed more and more TLDs. Keeping-up became a rat-race! Indeed, I've held another .info domain for twenty years, and used to suffer for my 'bleeding edge' daring - quite recently someone (who should remain name-less, and a few other less-es) sent me an email telling me how to log-in, but their log-in process wouldn't accept the 'illegal' address. Um... All together now: "a little bit of knowledge is a dangerous thing"! So what I was thinking was something like this: if type(email_recipient) != email.message.Message: I just don't know why that particular line isn't working. Will need more context. What is the objective? What is the source/pre-processing of these data-items. (etc) * Left-out .au, (a less important geo-TLD) to wind-up @Chris... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Too Broad of an exception
On 26/10/2023 04.49, rsutton via Python-list wrote: On 10/25/2023 11:06 AM, Stefan Ram wrote: r...@zedat.fu-berlin.de (Stefan Ram) writes: outer quotation marks) prints some prominent exception types. After ... "Manually removing" above was meant to be a fast first pass, where I only excluded exception types that were obviously inappropriate. It is now to be followed by a search for the appropriate exception types among those exception types left. @Rene & @Stefan, I really appreciate the guidance provided. By replacing Exception with ... It would appear that (at least one message) did not make it to email - neither to the list-archive. People wishing to learn are unable to benefit a response, if it is not sent to the list! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: return type same as class gives NameError.
On 23/10/2023 04.50, Antoon Pardon via Python-list wrote: I have the following small module: =-=-=-=-=-=-=-=-=-=-=-= 8< =-=-=-=-=-=-=-=-=-=-=-=-= from typing import NamedTuple, TypeAlias, Union from collections.abc import Sequence PNT: TypeAlias = tuple[float, float] class Pnt (NamedTuple): x: float y: float def __add__(self, other: PNT) -> Pnt: return Pnt(self[0] + other[0], self[1] + other[1]) =-=-=-=-=-=-=-=-=-=-=-= >8 =-=-=-=-=-=-=-=-=-=-=-=-= But when I import this, I get the following diagnostic: Traceback (most recent call last): File "", line 1, in File "/home/sisc/projecten/iudex/problem.py", line 10, in class Pnt (NamedTuple): File "/home/sisc/projecten/iudex/problem.py", line 14, in Pnt def __add__(self, other: PNT) -> Pnt: ^^^ NameError: name 'Pnt' is not defined. Did you mean: 'PNT'? Can someone explain what I am doing wrong? What happens when the advice is followed? Not sure why declare type-alias and then don't use it, but if insist on using class-name will be making a "forward-reference" (because class has not yet been fully defined) - see https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html#forward-references -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Where I do ask for a new feature
On 21/10/2023 01.32, Thomas Passin via Python-list wrote: On 10/19/2023 11:16 PM, Bongo Ferno via Python-list wrote: On Thursday, October 19, 2023 at 11:26:52 PM UTC-3, avi.e...@gmail.com wrote: There are many ways to make transient variables that disappear at some time and do we need yet another? Yes, you can create one of those ways but what is the big deal with deleting a variable when no longer used? Assigning a variable to something can be anything else than a temporal alias. A with statement makes clear that the alias is an alias and is local, and it automatically clears the variable after the block code is used. Python clutters the variable space with vars that are needed only on certain places, and an alias doesn't has a scope. Convenient alias are short names, and short names are limited in quantity. If the space is cluttered with short alias, it opens risks for wrong utilization. Its like writing a "for i" in a list comprehension and having to worry if "i" was already used in another place.. If a name is temporarily needed in a certain place and in a certain scope then reusing the name shouldn't be a problem. Agree. Surely, the only time we use a name like "i" is in a throw-away context? Under many circumstances Python will let us use "_" in place of a named-identifier - which enables both us and Python to remember its short-lived value/local-only use. Using an alias MERELY for the convenience of a shorter-name suggests two things: 1 lack of a competent editor/IDE, 2 lack of imagination in choosing names (perhaps one of THE skills of programming!) Yes, there are other languages which enforce a limited-scope on data-items created within or as part of a code-structure - and it IS a handy feature! On the other hand, Python's apposite stance can be useful too, eg trivial toy-example: # list_of_stuff = ... for n, element in list_of_stuff: if element == target: break # now element == target, so "element" is probably not that useful # but "n" is the index of the target-element, which may be # (there are other ways to accomplish same) Please take a look at the ideas behind "Modular Programming". This encourages the breaking-up of monolithic code and its "cluttered" global namespace, into potentially-independent code-units. The outlined-problem is solved by the independent scope of those code-units (in Python: modules, classes, functions, and "if __name__ == "__main__":". (to say nothing of the coder's virtues of "re-use", the "Single Responsibility Principle", "do one thing, and do it well", Law of Demeter, ...) Personal comment: my habit is to break specs into many classes and functions - sometimes more-so than others might prefer. Cannot recall when last had that hard-to-locate bug of unwittingly re-using a name/alias. (apologies: not a boast - a recommendation for going modular) -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: type annotation vs working code
On 04/10/2023 19.41, Chris Angelico via Python-list wrote: On Wed, 4 Oct 2023 at 15:27, dn via Python-list wrote: - should the class have been called either; class SomethingSingleton(): or a Singleton() class defined, which is then sub-classed, ie class Something( Singleton ): in order to better communicate the coder's intent to the reader? TBH, I don't think it's right to have a Singleton class which is subclassed by a bunch of different singletons. They aren't really subclasses of the same class. I could imagine Singleton being a metaclass, perhaps, but otherwise, they're not really similar to each other. I'm with you on this - should have made Singleton() an ABC. Yes, would only be a skeleton around which concrete singleton classes could be built. Like you, I v.rarely use them - but which means that the ABC is useful because it would save me from having to remember the curly-bits all-over-again... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: type annotation vs working code
On 02/10/2023 00.57, Karsten Hilbert via Python-list wrote:
Sorry for having conflated the core of the matter with all
the Borg shenanigans, that's where I found the problem in my
real code, so there :-)
The first question when dealing with the Singleton Pattern is what to do
when more than one instantiation is attempted:
- silently return the first instance
- raise an exception
The 'problem' interpreting the original code was that the 'Borg
Pattern', is not limited in number, but is where some class-attribute
list (or dict) is used to enable all instances to be aware of each of
the others (IIRC).
Is choosing names as important as selecting/implementing smart algorithms?
Consider this:
#
class Surprise:
def __init__(self, with_type_annotation=False):
if with_type_annotation:
try:
self.does_not_exist:bool
print('does_not_exist does exist')
except AttributeError:
print('does_not_exist does not exist')
return
try:
self.does_not_exist
print('does_not_exist does exist')
except AttributeError:
print('does_not_exist does not exist')
Surprise(with_type_annotation = False)
Surprise(with_type_annotation = True)
#
Is this how it is supposed to be ?
Wasn't this answered earlier? (@Mats)
That self.does_not_exist:bool isn't interpreted by Python to mean the
same as self.does_not_exist.
...and so we're addressing the important question: the try-test is for
existence, cf for
some value.
This can also be achieved by using the attribute in a legal expression, eg:
...
Might this remove the confusion (ref: @Mats):
self.already_initialized:bool == True
Not for me as that would _create_ already_initialized on the
instance. It would not allow me to test for it.
Which seems akin constructs for generating compatibility
between versions.
versions of ?
Of the language. Sometimes one tests for existence of a given
class in a module and defines said class oneself if it does
not exist. But that's leading astray.
What is the intent: a class where each instance is aware of every other
instance - yet
the word "Singleton" implies there's only one (cf a dict full of ...)?
The latter.
and so, returning to the matter of 'readability':
- the name "Borg" de-railed comprehension
- _instances:dict = {} implied the tracking of more than one
- should the class have been called either;
class SomethingSingleton():
or a Singleton() class defined, which is then sub-classed, ie
class Something( Singleton ):
in order to better communicate the coder's intent to the reader?
- from there, plenty of 'templates' exist for Singletons, so why do
something quite different/alien to the reader?
(thus concurring with @Richard: "tricky" subverts 'readability')
- is it better to use a technique which 'we' will recognise, or to ask
'us' to comprehend something 'new'?
(unless the 'new' is taking-advantage of a recent extension to the
language, eg switch; to justify 'trail-blazing' a
new/improved/replacement 'best practice')
- part of the 'tricky' seems to be an attempt to assess using an
instance-attribute, rather than a class-attribute. If the :bool (or
whichever) typing-annotation is added to a class-attribute (eg
_instance), will the problem arise?
- does the sequence
_instance = False
...
if not cls._instance:
ie the explicit version
if cls._instance == False:
measure 'existence' or a value?
- does the sequence
_instance = None
...
if not cls._instance:
ie the explicit version:
if cls._instance is None:
measure 'existence' or identity?
(indeed, are they more-or-less the same concept?)
- do the *attr() functions test for 'existence'?
(that said, most of the code-examples I spotted, in reading-up on this,
use either None or False - et tu Brute!)
Speaking of reading-up:
- am wondering where PEP 661 - Sentinel Values is 'going'?
- this article (https://python-patterns.guide/gang-of-four/singleton/)
mentions that the original GoF Singleton Pattern preceded Python
(particularly Python 3 classes). Also, that Python doesn't have
complications present in C++. It further discusses "several drawbacks",
which also champion 'readability' over 'trick' or 'sophistication'. I
think you'll enjoy it!
--
Regards,
=dn
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Re: type annotation vs working code
On 01/10/2023 11.25, Karsten Hilbert via Python-list wrote:
Am Sun, Oct 01, 2023 at 09:04:05AM +1300 schrieb dn via Python-list:
class WorkingSingleton(Borg):
def __init__(self):
print(self.__class__.__name__, ':')
try:
self.already_initialized
print('already initialized')
return
except AttributeError:
print('initializing')
self.already_initialized = True
self.special_value = 42
Where's the error in my thinking (or code) ?
What is your thinking?
Specifically, what is the purpose of testing self.already_initialized?
Apologies, my tending to use the "Socratic Method" with trainees (and
avoiding any concept of personal-fault with others), means it can be
difficult to tell if (personal*) introspection is being invited, or if I
don't know the answer (and want to).
* personal cf Python code introspection (hah!)
The purpose is to check whether the singleton class has been
... initialized :-)
The line
self.already_initialized = True
is misleading as to the fact that it doesn't matter at all
what self.already_initialized is set to, as long as is
exists for the next time around.
Isn't it generally regarded as 'best practice' to declare (and define a value
for) all
attributes in __init__()? (or equivalent) In which case, it will (presumably)
be defined
as False; and the try-except reworded to an if-else.
I fail to see how that can differentiate between first-call
and subsequent call.
+1
Alternately, how about using hasattr()? eg
if hasattr( self.already_initialized, 'attribute_name' ):
That does work. I am using that idiom in other children of
Borg. But that's besides the point. I was wondering why it
does not work the same way with and without the type
annotation.
Annotations are for describing the attribute. In Python we don't have
different instructions for declaring an object and defining it, eg
INTEGER COUNTER
COUNTER = 0
Thus, Python conflates both into the latter, ie
counter = 0
or
counter:int = 0
(both have the same effect in the Python Interpreter, the latter aims to
improve documentation/reading/code-checking)
Typing defines (or rather labels) the object's type. Accordingly, occurs
when the object is on the LHS (Left-hand Side) of an expression (which
includes function-argument lists).
In this 'test for existence': in the case of WorkingSingleton(), the
code-line is effectively only a RHS - see 'illegal' (below).
However, the annotation caused the code-line to be re-interpreted as
some sort of LHS in FailingSingleton().
- as explained (@Mats) is understood as a 'typing expression' rather
than 'Python code'.
Apologies: fear this a rather clumsy analysis - will welcome improvement...
try:
self.already_initialized
line is flagged by the assorted linters, etc, in my PyCharm as:
Statement seems to have no effect.
Well, the linter simply cannot see the purpose, which is
test-of-existence.
Question: is it a legal expression (without the typing)?
It borders on the illegal, I suppose, as the self-
introspection capabilities of the language are being
leveraged to achieve a legal purpose.
...and so we're addressing the important question: the try-test is for
existence, cf for some value.
This can also be achieved by using the attribute in a legal expression, eg:
self.already_initialized == True
When introspecting code, if type-checkers cannot determine the purpose,
is there likely to be a 'surprise factor' when a human reads it?
(that's Socratic! I already hold an opinion: right or wrong)
Might this remove the confusion (ref: @Mats):
self.already_initialized:bool == True
(not Socratic, don't know, haven't tested)
Which seems akin constructs for generating compatibility
between versions.
versions of ?
It seems the answer is being pointed to in Matts response.
It just mightily surprised me.
Me too!
I am slightly confused (OK, OK!) and probably because I don't have a
good handle on "Borg" beyond knowing it is a Star Wars?Trek reference
(apologies to the reader sucking-in his/her breath at such an utterance!).
What is the intent: a class where each instance is aware of every other
instance - yet the word "Singleton" implies there's only one (cf a dict
full of ...)?
Second move (also, slightly) off-topic:
I'm broadly in-favor of typing; additionally noting that trainees find
it helpful whilst developing their code-reading skills. However, am not
particularly zealous in my own code, particularly if the type-checker
starts 'getting picky' with some co
Re: type annotation vs working code
On 01/10/2023 08.00, Karsten Hilbert via Python-list wrote:
A type annotation isn't supposed to change what code does,
or so I thought:
#
class Borg:
_instances:dict = {}
def __new__(cls, *args, **kargs):
# look up subclass instance cache
if Borg._instances.get(cls) is None:
Borg._instances[cls] = object.__new__(cls)
return Borg._instances[cls]
class WorkingSingleton(Borg):
def __init__(self):
print(self.__class__.__name__, ':')
try:
self.already_initialized
print('already initialized')
return
except AttributeError:
print('initializing')
self.already_initialized = True
self.special_value = 42
class FailingSingleton(Borg):
def __init__(self):
print(self.__class__.__name__, ':')
try:
self.already_initialized:bool
print('already initialized')
return
except AttributeError:
print('initializing')
self.already_initialized = True
self.special_value = 42
s = WorkingSingleton()
print(s.special_value)
s = FailingSingleton()
print(s.special_value)
#
Notice how Working* and Failing differ in the type annotation
of self.already_initialized only.
Output:
WorkingSingleton :
initializing
42
FailingSingleton :
already initialized <==
Huh ?
Traceback (most recent call last):
File
"/home/ncq/Projekte/gm/git/gnumed/gnumed/client/testing/test-singleton.py", line 48,
in
print(s.special_value)
^^^
AttributeError: 'FailingSingleton' object has no attribute
'special_value'
Where's the error in my thinking (or code) ?
What is your thinking?
Specifically, what is the purpose of testing self.already_initialized?
Isn't it generally regarded as 'best practice' to declare (and define a
value for) all attributes in __init__()? (or equivalent) In which case,
it will (presumably) be defined as False; and the try-except reworded to
an if-else.
Alternately, how about using hasattr()? eg
if hasattr( self.already_initialized, 'attribute_name' ):
# attribute is defined, etc
As the code current stands, the:
try:
self.already_initialized
line is flagged by the assorted linters, etc, in my PyCharm as:
Statement seems to have no effect.
Unresolved attribute reference 'already_initialized' for class
'WorkingSingleton'.
but:
self.already_initialized:bool
passes without comment (see @Mats' response).
Question: is it a legal expression (without the typing)?
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: path to python in venv
On 28/09/2023 09.32, Jon Ribbens via Python-list wrote: On 2023-09-27, Larry Martell wrote: On Wed, Sep 27, 2023 at 12:42 PM Jon Ribbens via Python-list wrote: On 2023-09-27, Larry Martell wrote: I was under the impression that in a venv the python used would be in the venv's bin dir. But in my venvs I see this in the bin dirs: lrwxrwxrwx 1 larrymartell larrymartell7 Sep 27 11:21 python -> python3 lrwxrwxrwx 1 larrymartell larrymartell 16 Sep 27 11:21 python3 -> /usr/bin/python3 ... Not sure what this really means, nor how to get python to be in my venv. WHy do you want python to be "in your venv"? Isn't that the entire point of a venv? To have a completely self contained env? So if someone messes with the system python it will not break code running in the venv. The main point of the venv is to isolate the installed packages, rather than Python itself. I'm a bit surprised your symlinks are as shown above though - mine link from python to python3.11 to /usr/bin/python3.11, so it wouldn't change the version of python used even if I installed a different system python version. "venv — Creation of virtual environments" (https://docs.python.org/3/library/venv.html) starts by saying: «The venv module supports creating lightweight “virtual environments”, each with their own independent set of Python packages installed in their site directories.» but later expands this with: «Used to contain a specific Python interpreter...» even though the primary use-case treats the system interpreter as the "base" Python/environment. Time for some reading and proving appropriate combinations of options? Over the years there have been various proposals to enable multiple versions of Python to exist concurrently on a single machine, notably Python2 + Python3 - but am failing to recall any official docs on Python3.n + Python3.m; eg "PEP 554 – Multiple Interpreters in the Stdlib" (https://peps.python.org/pep-0554/). That said there's plenty of articles on-line (which may/not feature venv*) such as "Multiple Python interpreters" (https://developer.fedoraproject.org/tech/languages/python/multiple-pythons.html) * although the OP didn't mention an OpSys, one poster did mention Fedora-Linux... NB some of this info may be dated - it is some time since conducted this investigation (and decided not to use venv - apologies!) Am currently using PyCharm (courtesy of recent teams' conventions) and it eases both problems (which interpreter, and which development-environment/activation steps) but in automating 'the boring stuff' it will be interesting to see if in-future, I notice when the project is based upon an older system! FYI https://www.jetbrains.com/help/pycharm/installing-uninstalling-and-reloading-interpreter-paths.html (I'd be surprised if the other major tool-sets don't offer something similar) Disclaimer: JetBrains sponsor our local PUG-meetings with a door-prize. -- -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Python Launcher Pops Up When Py-based App Is Running (Mac)
On 17/09/2023 13.20, James Greenham via Python-list wrote: Hello, On the face of it, the Python-Mac mailing list is largely inactive so I'm posting here since it looks like this one is livelier. What happens when doGrab() is called from the REPL, after being 'fed' data you expect is valid? (per a unit-test) What code-level debugging has been exercised? Have you tried running the code in a debugger, in order to step into the (assumed) doGrab error? Sadly, this code is so old as to have grown whiskers. - are all the called-modules, eg webkit and the OpSys; still offering the appropriate interfaces, and continuing to behave in the expected fashion? (anything relevant in those Release Notes?) - in theory, Python 2 will still run. However, a reasonable proportion of today's Python-coders are unlikely to have ever used it. (Sunsetting Python 2 https://www.python.org/doc/sunset-python-2/) - were this code to be written using today's libraries, it is unlikely to look anything like this (which may also be contributing to the dearth of replies) -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
ANN: Wed 20 Sep: Terminal-based user interfaces (TUIs) with ease using Textual
Rodrigo's back! Fresh from his successes at EuroPython... You are invited to join the next virtual NZPUG Auckland Branch meeting (Wed 20 Sep, 1830~2030 local, ie 0630~0830 UTC) Learn how to build powerful terminal-based user interfaces (TUIs) with ease using Textual - an open-source Python framework. Through this tutorial, you'll learn how to use features like Textual's built-in widgets, reactive attributes, and message-passing system, to start developing a simple TODO app that runs directly in your terminal. About Rodrigo Girão Serrão: Rodrigo has presented to NZPUG Auckland Branch previously. He speaks frequently at various PyCons (Python Conferences) and other gatherings. As well as Python, he has been playing with APL, C++, and more. Combining programming and maths, he describes himself as a mathemagician. Rodrigo has always been fascinated by problem solving and that is why he picked up programming – so that he could solve more problems. He also loves sharing knowledge, and that is why he spends so much time writing articles in his blog, writing on Twitter, and giving workshops and courses. During the week, Rodrigo can be found banging his head against the wall while trying to solve a Textual bug, as he works on Textual full-time. To RSVP (to receive the meeting-URL) and for more detail: https://www.meetup.com/nzpug-auckland/events/295433884/ The Auckland branch of the New Zealand Python Users Group meets twice monthly. You're very welcome to attend online or in-person (as available). Meeting location-details or URL will be sent to those who RSVP. We are a healthy mix of Python users. Students, academics, hobbyists, industry professionals, and many completely new to Python. The 'room' opens at 1815 (local time) with an opportunity to network with colleagues. Formal start is 1830. Aiming to finish by 2030. We are always keen to hear suggestions for meeting-topics, and to meet with folk who'd like to present or lead - eg a brief lightning talk, a practical coaching-session, a full lecture... Help is available if you've never done such a thing before! We follow the NZPUG Code of Conduct to create an inclusive and friendly environment. We express thanks to, and encourage you to investigate our sponsors: Catalyst Cloud, New Zealand Open Source Society, JetBrains, and IceHouse Ventures. -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Co-op Group: Django web framework
Are you interested in learning Django? Would like to improve your Django knowledge and skills? Have you been picking-up Django piecemeal, and need to consolidate and clarify? Do you know some Django and would like to acquire mentoring and coaching skills? If so, please join us to form a Learning Django Co-op. RSVP at https://www.meetup.com/nzpug-auckland/events/295727130/ -- Regards =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Context manager for database connection
On 24/08/2023 06.11, dn via Python-list wrote:
On 24/08/2023 03.41, Jason Friedman via Python-list wrote:
with Database() as mydb:
conn = mydb.get_connection()
cursor = conn.get_cursor()
cursor.execute("update table1 set x = 1 where y = 2")
cursor.close()
cursor = conn.get_cursor()
cursor.execute("update table2 set a = 1 where b = 2")
cursor.close()
import jaydebeapi as jdbc
class Database:
database_connection = None
def __init__(self, auto_commit: bool = False):
self.database_connection = jdbc.connect(...)
self.database_connection.jconn.setAutoCommit(auto_commit)
def __enter__(self) -> jdbc.Connection:
return self
def __exit__(self, exception_type: Optional[Type[BaseException]],
exception_value: Optional[BaseException],
traceback: Optional[types.TracebackType]) -> bool:
if exception_type:
self.database_connection.rollback()
else:
self.database_connection.commit()
self.database_connection.close()
def get_connection(self) -> jdbc.Connection:
return self.database_connection
Using a context-manager is a good idea: it ensures clean-up with/without
an exception occurring. Accordingly, I (and may I presume, most) like
the idea when working with life-cycle type resources, eg I/O. Absolutely
nothing wrong with the idea!
However, the scope of a c-m is the with-block. If there are a number of
'nested operations' to be performed (which could conceivably involve
other c-ms, loops, or similar code-structures) the code could become
harder to read and the length of the scope unwieldy.
An ease of management tactic is being able to see the start and end of a
construct on the same page/screen. Such would 'limit' the length of a
c-m's scope.
Perhaps drawing an inappropriate parallel, but like a try-except block,
there seems virtue in keeping a c-m's scope short, eg releasing
resources such as a file opened for output, and some basic DBMS-es which
don't offer multi-access.
Accordingly, why I stopped using a c-m for database work. NB YMMV!
There were two other reasons:
1 multiple databases
2 principles (and my shining virtue (?) )
1 came across a (statistics) situation where the client was using two
DBMS-es. They'd used one for some time, but then preferred another. For
their own reasons, they didn't migrate old data to the new DBMS. Thus,
when performing certain analyses, the data-collection part of the script
might have to utilise different DB 'sources'. In at least one case,
comparing data through time, the routine needed to access both DBMS-es.
(oh what a tangled web we weave...)
2 another situation where the script may or may not actually have needed
to access the DB. Odd? In which case, the 'expense' of the 'entry' and
'exit' phases would never be rewarded.
Thus, 'inspired' to realise that had (long) been contravening SOLID's
DSP advice?rule (Dependency Inversion Principle).
Accordingly, these days adopt something like the following (explaining
it 'backwards' to aid comprehension in case you (gentle reader) have not
come-across such thinking before - remember that word, "inversion"!)
- in the mainline, prior to processing, instantiate a database object
database = Database( credentials )
- assume the mainline calls a function which is the substance of the script:
def just_do_it( database_instance, other_args, ):
while "there's work to be done":
database.query( query, data, etc, )
# could be SELECT or UPDATE in and amongst the 'work'
- a basic outline of query() might be:
def query( self, sql, data, etc, ):
cursor = self.get_cursor()
cursor.execute( sql, data, ) # according to DB/connector, etc
# return query results
- a query can't happen without a "cursor", so either use an existing
cursor, or create a fresh one:
def get_cursor( self ):
if not self._cursor:
connection = self.get_connection()
self._cursor = connection.cursor()
return self._cursor
NB assuming the DBMS has restrictions on cursors, I may have multiple
connections with one cursor each, but in some situations it may be
applicable to run multiple cursors through a single connection.
- a cursor can't exist without a "connection", so either ... :
def get_connection( self ):
if not self._connection:
self._connection = # connect to the DB
return self._connection
- to instantiate a DB-object in the first place, the class definition:
class Database:
def __init__(self):
self._connection = None
self._cursor = None
- and the one part of the exposition that's not 'backwards&#x
Re: Context manager for database connection
On 24/08/2023 03.41, Jason Friedman via Python-list wrote:
I want to be able to write code like this:
with Database() as mydb:
conn = mydb.get_connection()
cursor = conn.get_cursor()
cursor.execute("update table1 set x = 1 where y = 2")
cursor.close()
cursor = conn.get_cursor()
cursor.execute("update table2 set a = 1 where b = 2")
cursor.close()
I'd like for both statements to succeed and commit, or if either fails to
stop and for all to rollback.
Is what I have below correct?
import jaydebeapi as jdbc
class Database:
database_connection = None
def __init__(self, auto_commit: bool = False):
self.database_connection = jdbc.connect(...)
self.database_connection.jconn.setAutoCommit(auto_commit)
def __enter__(self) -> jdbc.Connection:
return self
def __exit__(self, exception_type: Optional[Type[BaseException]],
exception_value: Optional[BaseException],
traceback: Optional[types.TracebackType]) -> bool:
if exception_type:
self.database_connection.rollback()
else:
self.database_connection.commit()
self.database_connection.close()
def get_connection(self) -> jdbc.Connection:
return self.database_connection
Looking good!
Assuming this is the only DB-interaction, a context-manager seems
appropriate. If the real use-case calls for more interactions, the cost
of establishing and breaking DB-connections becomes a consideration.
Alternately, the 'length'?'life' of the context-manager *might*
complicate things.
Intriguing that given such a start, the code doesn't feature a
context-manager for a query.
That two cursors are established is also a 'cost'. Could both queries
utilise the same cursor?
(in which case, could consider adding to __init__() or __enter__(), and
close in __exit__() )
Because the context-manager has been implemented as a class, there is no
reason why one can't add more methods to that class (it doesn't need to
be limited to the functional __enter__() and __exit__() methods!
Indeed there is already get_connection(). Why not also a query( self,
sql-code ) method?
These might reduce the mainline-code to something like:
if __name__ == "__main__":
with Database() as mydb:
mydb.query( "update table1 set x = 1 where y = 2" )
mydb.query( "update table2 set a = 1 where b = 2" )
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: Imports and dot-notation
On 09/08/2023 22.30, Oliver Schinagl via Python-list wrote: ...> Looking at a python projects code and repository layout, we see the following directory structure. /project/core /project/components/module1 ... /project/components/moduleN /projects/util ...> Some modules import other modules, and I see (at the very least) two (kind of three?) different ways of doing so. `from project.components.module1 import function1, function2 as func, CONST1, CONST2 as CONST` or maybe even (which has as an advantage that it becomes clear which namespace something belongs to `from project.components.module1 import function1, function2 as module1_function2, CONST1, CONST2 as MODULE1_CONST2` but then it really just becomes personal preference, as the number of characters saved on typing is almost negative (due to having a more complex import). but also the dot notation being used `from project.components import module1` where obviously the functions are invoked as `module1.function1` etc Firstly, the path followed will depend upon the starting position! Keep reading and you should come across a reference to 'hobgoblin of little minds'. What should we be concentrating on/about? If 'naming' is a great (?the greatest) challenge of programming, surely remembering the names of classes, methods, functions, modules, etc; follows... (and by implication, as you've illustrated, perhaps where they come-from), ie code is read more often than it is written, so think about comprehension rather than typing! If one (one's team!) frequently uses a module, then a jargon may develop. For example: import numpy as np ... a = np.arange(6) In which case, those au-fait with the jargon know that the "np." prefix tells them where "arange()" can be found - conversely, that if the IDE doesn't alert, that np/numpy must be (first) import-ed. However, there is a cognitive-load to 'translate' "np" into "numpy". Not much, but then over-load is not a single thought but the combination of 'everything'. The second option (OP) is very (laboriously) clear in mapping the source of each function or constant. By way of comparison then, the code may now appear cluttered, because there's so much text to read. There would be less if an abbreviation were used. The dev.tool in-use may also influence this decision. If hovering-over an identifier reveals source-information, what value the extra code? Intelligent completion also reduces relevance of 'number of characters saved on typing'. Accordingly, give frequently-used functions/modules the abbreviation treatment -but only if YOU feel it right. Otherwise, use a longer-form to improve readability/comprehension. THE answer will thus vary by library/package/module, by application, and by coder (jargon works best if 'all' use it/understand same). Side note: Using "...import identifier, ..." does not save storage-space over "import module" (the whole module is imported regardless, IIRC), however it does form an "interface" and thus recommend leaning into the "Interface Segregation Principle", or as our InfoSec brethren would say 'the principle of least privilege'. Accordingly, prefer "from ... import ... as ...". -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Planning a Python / PyData conference
Hi Wilber, On 09/08/2023 14.28, Wilber H via Python-list wrote: Hi, I would like to plan a Python / PyData conference in the country of the Dominican Republic, and would like your feedback on how to best plan for the conference. Recommend making your request of the folks who organise EuroPython and/or PyConUS - and then same for smaller gatherings. (would suggest to ours, but those folk are already over-loaded to be ready in a few weeks' time) -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Mtg ANN: Using computer vision AI to help protect the worlds rarest dolphin
Wed 16 Aug 2023, 1800~20:30 NZST (0600~0830 UTC, late-Tue in US) Details and RSVP at https://www.meetup.com/nzpug-auckland/events/295091858/ Teaching a computer to see. How computer vision is helping to protect the world’s rarest dolphin and how you can train your own model. Tane van der Boon will talk about the MAUI63 project, and then lead us through how to train and utilise a custom computer vision object detector. Essentially allowing our software to be able to see. MAUI63 was given its name because when the venture began, there were only 63 Māui dolphins left in existence. Using drone technology and AI to collect and process visual data, the founders took action to collect data to help save the world’s rarest dolphin from extinction and influence future marine conservation efforts. The MAUI63 team uses a customised drone to find and track the movement of dolphins, and enables individual dolphins to be identified through their fin markings. The information collected can then be used to inform better data driven decisions on how best to protect them. Later, Tane will lead us through a smaller task to build our own image recognizer. (more details in due course...) The Auckland Branch of the New Zealand Python Users' Group meet twice monthly. You're very welcome to attend online or in-person (as available). Meeting location-details or URL will be sent to those who RSVP. We are a healthy mix of Python users. Students, academics, hobbyists, industry professionals, and many completely new to Python. The "room" opens at 1800 (local time) with an opportunity to network with colleagues. Everything should be wrapped up by 2030. We are always keen to hear suggestions for meeting-topics, and to meet with folk who'd like to present or lead - eg a brief lightning talk, a practical coaching-session, a full lecture... Help is available if you've never done such a thing before! We follow the NZPUG Code of Conduct (https://python.nz/code-of-conduct) to create an inclusive and friendly environment. We express thanks to, and encourage you to investigate, our sponsors: Catalyst Cloud, New Zealand Open Source Society, JetBrains, and IceHouse Ventures. -- Regards =dn -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Where is the error?
On 07/08/2023 08.41, Peter J. Holzer via Python-list wrote: Mostly, error messages got a lot better in Python 3.10, but this one had me scratching my head for a few minutes. ... The error message is now a lot better, of course, but the fact that it points at the expression *before* the error completely threw me. The underlined expression is clearly not missing a comma, nor is there an error before that. My real program was a bit longer of course, so I checked the lines before that to see if I forgot to close any parentheses. Took me some time to notice the missing comma *after* the underlined expression. Is this "clairvoyant" behaviour a side-effect of the new parser or was that a deliberate decision? Found myself chuckling at this - not to be unkind, but because can easily imagine such confusion on my own part. The issue of unhelpful error messages or information aimed at a similar but different context, has been the story of our lives. Advice to trainees has always been to cast-about looking for the error - rather than taking the line-number as a precise location. Have made a note to avoid advising folk to work 'backwards'! Meantime (back at the ranch?), haven't experienced this. Using an IDE means all such stuff is reported, as one types, through highlights and squiggly lines (which should(?) be considered and cleared - before pressing the GO-button). In this case, the PyCharm* editor adds red-squiggles where the commas should have been. Hovering the cursor over a squiggle, the IDE reports "',' expected"! Its PythonConsole behaves similarly (without offering a 'hover'). Plus, even after the closing brace, it continues to assume a multi-line compound-statement (and thus won't execute, per expected REPL behavior). Way-back (grey-beard time!) when we submitted card-decks of code to be compiled over-night, one idea to avoid expensive, trivial errors/eras; was that spelling-checkers should be built-in to compilers, eg to auto-magically correct typos, eg AFF 1 TO TOTAL instead of: ADD 1 TO TOTAL These days, we can look at code from two or more years ago, 'produced' by ChatGPT (et al), aka "The Stochastic Parrot". There is some thought that artificial 'intelligence' will one-day be able to do the coding for us/predict what is required/act as a crystal ball... Speaking of which, and just because I could, here's what Chat-GPT had to say when I asked "what's wrong with ...": «The issue in the given Python code is that you're missing commas between the key-value pairs in the dictionary. Commas are required to separate different key-value pairs within a dictionary. Here's the corrected version of the code: ... » Question: If a Chat-AI is built into the IDE (I stripped such out from mine), does it take-over error reporting and diagnosis (and offer the option of replacing with its 'corrected version'?) - rather than requiring an extra copy-paste step, per above? (and need for my assumption of where the error is located) Hope you've exerted copyright over the "clairvoyant" description! * JetBrains kindly sponsor our PUG with a monthly door-prize. -- -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: isinstance()
On 05/08/2023 11.18, Chris Angelico via Python-list wrote:
On Sat, 5 Aug 2023 at 09:08, dn via Python-list wrote:
On 03/08/2023 11.38, Jon Ribbens via Python-list wrote:
On 2023-08-02, dn wrote:
Can you please explain why a multi-part second-argument must be a tuple
and not any other form of collection-type?
The following comment may hold a clue:
if (PyTuple_Check(cls)) {
/* Not a general sequence -- that opens up the road to
recursion and stack overflow. */
https://github.com/python/cpython/blob/main/Objects/abstract.c#L2684
Plus an almost total lack of demand for change I should think.
Thanks for the reference!
Am not proposing a change (have learned 'the rule' and accepted
life-as-it-is), but was curious about the restriction: why not any
(reasonable sequence)?
There are quite a few places where the only option is a tuple.
"spam".startswith(["sp", "h"])
Traceback (most recent call last):
File "", line 1, in
TypeError: startswith first arg must be str or a tuple of str, not list
try: 1/0
... except [ValueError, IndexError]: pass
...
Traceback (most recent call last):
File "", line 1, in
ZeroDivisionError: division by zero
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "", line 2, in
TypeError: catching classes that do not inherit from BaseException is
not allowed
It simplifies a lot of checks. Either it's a tuple or it's a single
thing. A *lot* of values are iterable, but only tuples are tuples.
As the C comment notes, this also means you don't have to worry about
recursion; otherwise, even core language features like exception
handling would have to iterate over a thing while ensuring that they
don't get stuck in self-referential objects. (Incidentally, it seems
that exception handling doesn't bother with recursion *at all*, and
won't catch "(a, (b, c))" - but even if recursion is handled, it can't
go infinite, short of some serious messing around in ctypes or the C
API.)
Yes. Thanks Chris!
The idea that such 'lists' be immutable (even, hashable), and therefore
a tuple, makes a certain amount of sense, and @Cameron mentioned
'frugality'.
My limitation is thinking only at the Python level (which as @Jon
pointed-out, is only part of the story).
Faced with a situation where an argument may be a scalar-value or an
iterable, I'll presume the latter, eg throw it straight into a for-loop.
If that fails (because the argument is a scalar), use try-except to
re-route the logic. Alternately, in an OOP situation, utilise
polymorphism so that the 'scalar' and 'iterable' instances both include
the appropriate method[name]. Accordingly, as long as the argument is an
iterable (includes an __iter__() method), the actual type/class is
more-or-less irrelevant.
However, as observed earlier - and with these additions, having learned
the 'rule', ie use a tuple; the brain is still pondering, but have
shrugged-shoulders and carried-on regardless...
--
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: isinstance()
On 03/08/2023 11.38, Jon Ribbens via Python-list wrote:
On 2023-08-02, dn wrote:
Can you please explain why a multi-part second-argument must be a tuple
and not any other form of collection-type?
The following comment may hold a clue:
if (PyTuple_Check(cls)) {
/* Not a general sequence -- that opens up the road to
recursion and stack overflow. */
https://github.com/python/cpython/blob/main/Objects/abstract.c#L2684
Plus an almost total lack of demand for change I should think.
Thanks for the reference!
Am not proposing a change (have learned 'the rule' and accepted
life-as-it-is), but was curious about the restriction: why not any
(reasonable sequence)?
Such pondering continues in my subversive mind, given such thoughts as:
- "we're all adults here"
(eg frequent justification when arguing about Python not having "private
attributes" per-se).
So, if we introduce a complexity, on our own heads be it!
(hardly likely given that all we are likely to attempt is the
application of a simple and short 'list' of [un]acceptable types).
NB understood that the quoted-code is applied in many and other 'scalar
or tuple' situations.
- Python happily enables recursion, which "opens up the road to
recursion and stack overflow.".
So, why install a 'nanny' to save us from ourselves here?
Again: seems on-the-surface that such 'lists' (at the code-line level)
will be mono-dimensional 99.9% of the time.
NB having said that, the underlying mechanism *is* multi-dimensional:
"direct, indirect, or virtual) subclass thereof"
(https://docs.python.org/3/library/functions.html#isinstance)
Further: the 'rules' say: "classinfo is a tuple of type objects (or
recursively, other such tuples)". Thus, can write:
>>> target_object = ...
>>> inner_tuple = float, complex
>>> inner_tuple
(, )
>>> isinstance( target_object, ( str, inner_tuple, int, ), )
False
I can't say I've ever used such construction in-the-wild - either
defining and then using an "inner_tuple", or even nesting. YMMV!
Any thoughts?
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
Re: How to find the full class name for a frame
On 04/08/2023 15.34, Jason Friedman via Python-list wrote:
import inspect
def my_example(arg1, arg2):
print(inspect.stack()[0][3])
my_frame = inspect.currentframe()
args,_,_,values = inspect.getargvalues(my_frame)
args_rendered = [f"{x}: {values[x]}" for x in args]
print(args_rendered)
my_example("a", 1)
The above "works" in the sense it prints what I want, namely the method
name (my_example) and the arguments it was called with.
The above didn't 'work' - please copy-paste and ensure that the
email-client is respecting indentation.
My question is: let's say I wanted to add a type hint for my_frame.
my_frame: some_class_name = inspect.currentframe()
What would I put for some_class_name?
"frame" (without quotations) is not recognized,
Nor is inspect.frame.
We know Python code is executed in an execution frame.
(https://docs.python.org/3/reference/executionmodel.html?highlight=frame)
We are told "Frame objects Frame objects represent execution frames."
(https://docs.python.org/3/reference/datamodel.html?highlight=frame).
The word "represent" conflicts with the idea of "are".
'Under the hood' inspect calls sys._current_frames()
(https://docs.python.org/3/library/sys.html?highlight=frame). That code is:
def _getframe(*args, **kwargs): # real signature unknown
"""
Return a frame object from the call stack.
If optional integer depth is given, return the frame object that many
calls below the top of the stack. If that is deeper than the call
stack, ValueError is raised. The default for depth is zero, returning
the frame at the top of the call stack.
This function should be used for internal and specialized purposes
only.
"""
pass
Which rather suggests that if the sys library doesn't know the
signature, then neither typing nor we mere-mortals are going to do so,
either.
Theory: the concept of a frame does not really exist at the Python-level
(remember "represents"). Frames (must) exist at the C-level
(https://docs.python.org/3/c-api/frame.html?highlight=frame#c.PyFrameObject)
of the virtual-machine - where typing is not a 'thing'.
It's an interesting question. Perhaps a better mind than mine can give a
better answer?
--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list
isinstance()
Can you please explain why a multi-part second-argument must be a tuple and not any other form of collection-type? The signature is: isinstance(object, classinfo) leading to "classinfo" of: 1/ a single class/type, eg int 2/ a tuple of same, eg ( int, str, ) 3/ a union type, eg int | str (v3.10+) A question was asked about this at last night's PUG-meeting. The person was using the union option, but from Python v3.8. Sorting that out, he replaced the union with a list. No-go! Before correcting to a tuple... Why does the second argument need to be a tuple, given that any series of non-keyword arguments is a tuple; and that such a tuple will still need to be delimited by parentheses. In other words, other forms of delimiter/collection, eg list and set; being a series of elements/members would seem no different. Yes, the underlying C operation appears to only accept a single argument (am not C-soned, mea culpa!). There is some discussion about hashability, but isn't it coincidental rather than constructive? (again, maybe I've not understood...) Enquiring minds want to know... Web.Refs: https://docs.python.org/3/library/functions.html?highlight=isinstance#isinstance https://docs.python.org/3/c-api/object.html?highlight=isinstance#c.PyObject_IsInstance https://docs.python.org/3/reference/datamodel.html?highlight=isinstance -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Hybrid meeting ANN: Using properties and descriptors
This month's meeting (Wed 19 July, 1800 for 1830 NZST = 0600/0630 UTC) will cover more-advanced OOP Python skills. You will be most-welcome to join us... "Using properties and descriptors" will look at a series of code-examples exploring problems and how these constructs offer solutions. The presentations are in lecture-style. If there's time (or for later study), some coding workshops will be suggested. Prerequisite knowledge or experience for "Properties": Object-Oriented Programming (in Python), coding custom-classes, using available decorators, some experience in data organisation/design, PEP-008 and coding styles, and reading type-hints. Prerequisite knowledge or experience for "Descriptors": "Properties" topic in this series, coding custom-classes with 'magic methods', implementing inheritance and composition, design-experience in data organisation, Object-Oriented Design, decent understanding of OOP philosophy. Hints: A lab-/log-book will be useful for taking notes. A headset will ease asking questions, answering questions, and discussion. Python IDE ready for coding. Two choices for attendance: online or in-person (Parnell, Auckland). Please RSVP to book-in and receive access information:- - Remote attendance RSVP: https://www.meetup.com/nzpug-auckland/events/njdjssyfckbzb/ - In-person RSVP to https://www.meetup.com/nzpug-auckland/events/294745326/ You are cordially invited to join us! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: my excel file is not updated to add new data
r is simplified (in fact, the "testability" advantage may solve this problem - or in a new-design situation, avoid it*) Testing the function is carried-out by calling the function with a variety of example input-data, and ensuring the result is what you expect/want/require. Thus: chemin = create_data_path( "testpython.xlsx" ) assert "chemin\testpython.xlsx" == chemin, "Not equal, but should be" [for non-French speakers: chemin = path ] (an assert statement says: if the condition is False, print an optional message, and raise an exception/stop processing) similarly: chemin = create_data_path( "testpython.xlsx" ) assert "path_to_project\niaiserie.xlsx" != chemin, "Should not be equal" [for non-French speakers: niaiserie = some random name/silliness ] Such tests should not be written as one-off code (the way one might add debug-printing - and then take it out again). If you ever have need to copy such functions into other projects (eg create_data_path(), then you'll want to copy the tests as well, to ensure everything works in the new scenario! Accordingly, create a new .py file, with "test_" plus the name of the existing code-file. Inside that, import the code-file. The code the tests in the test file, to run each function in-turn (and several times, with different data), to assure the function in the code-file. (yes, if you see virtue in this approach, there are some very helpful libraries to ease testing and automate it (better to have the machine do the work, rather than you have to (keep) doing it!), eg pytest (py.test) - worth some investigation time?) What has been achieved? By the time you've tested the first few functions, you will know whether or not existing files are being (correctly) used as 'base data'. Continuing 'down', you will discover if new data is being correctly added/updating existing data. Further on, you will find if the output is being correctly written to that file. Sooner or later, you will have answered the "where is the error?" problem 'here'! You will also have noticed any similar errors which may be 'hiding' in the code, unnoticed (so far!)... (and all without needing to ask someone-else for help) * not entirely true. In this manner, each function can be relatively-well proven with "unit tests". There is however, an additional source of error: do the functions 'play well together'? Ensuring this happens is the objective of another type of test: "integration testing". For example, does check_for_file() work with the output from the preceding stage: create_data_path()? Yes, these sorts of tests could be included at the bottom of the 'unit test' script, or written in a separate test-file... Not forgetting, the "mainline" of the production program[me] needs to be written! It will call each function in-turn, feeding specific data into (at least) the first, eg which Excel file? Thereafter, likely feeding output from earlier functions into later processing. Until, 'the end'. Fin! NB the "mainline" will be a collection and compression of the imperatives which could be copied from any "integration testing". NBB what I call the "mainline" (a throw-back to my training, so long ago it is lost in the mists of time...) fits into a Python idiom: if __name__ == "__main__": print( "\nMy wonderful program\n" ) # you'll do this in the GUI intermediate_result_1 = function1() intermediate_result_1 = function2( intermediate_result_1 ) ... NB it seems long-winded (and my IDE often grumbles about this too!) but I often prefer creating 'intermediate results' rather than writing 'earlier' functions as parameters to 'later' functions. If any thing goes wrong (how could it, after all that testing?) it's easier to answer that famous question: "where is the error?". That said: there are exceptions to every 'rule' - and YMMV! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Python Issue
On 22/06/2023 03.28, Pickle Pork via Python-list wrote: Python is unable to open. Exit Code: 1 This is not good. Please give some useful information: - from where did you download Python? - which operating system? - how do you "open" Python? etc. -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
