Fwd: A typing question
Do you want the following? ``` from typing import List, Optional class GLOBALS: foos: Optional[Foos] = None class Foo: def __init__(self): pass class Foos: Foos: List[Foo] = [] def __init__(self): pass GLOBALS.foos = Foos() ``` Kind regards, Sam Ezeh On Sat, 29 Oct 2022 at 22:13, Paulo da Silva < p_d_a_s_i_l_v_a...@nonetnoaddress.pt> wrote: > Hi! > > Consider this simple script ... > > ___ > from typing import List, Optional > > class GLOBALS: > foos=None > > class Foo: > > def __init__(self): > pass > > class Foos: > Foos: List[Foo]=[] > # SOME GLOBALS ARE USED HERE in a real script > > def __init__(self): > pass > > GLOBALS.foos: Optional[Foos]=Foos() > ___ > > Running mypy on it: > pt9.py:18: error: Type cannot be declared in assignment to non-self > attribute > pt9.py:18: error: Incompatible types in assignment (expression has type > "Foos", variable has type "None") > Line 18 is last line and pt9.py is the scrip. > > Replacing last line by > GLOBALS.foos=Foos() > and running mypy still gives the second error. > pt9.py:18: error: Incompatible types in assignment (expression has type > "Foos", variable has type "None") > > What is the common practice in these cases? > > Thank you. > > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
Re: Virtual PUG-meeting: An applied introduction to Finite State Machines
That seems interesting. Is this hosted online? And are there any suggested reading materials for those who might not be able to attend? Kind regards, Sam Ezeh On Tue, 13 Sept 2022 at 22:53, dn wrote: > An applied introduction to Finite State Machines > 0730 UTC, Wed 21 Sep 2022 > > The basics of Finite State Machines and what they are good for. How to > use FSM for solving optimization problems. > > - A simple traffic jam > - A bigger traffic jam > - A sudoku > > After this lecture there won't be any discrete optimization problem you > won't be able to solve. > > Dr. Bjorn Madsen solves optimization problems using Python, for DoD, > LEGO, Coca Cola, Airbus and many other companies. > > > These meetups have two sessions. At least one is aimed at a beginner > level - in either Python or FSMs. > > Sign-up and more details from https://www.meetup.com/nzpug-auckland/ > -- > Regards, > =dn > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
Re: Building on Windows
To add to this, my process was 1. Setup the VM 2. Install Git 3. Clone CPython 4. Run `PCbuild\build.bat -d -e` 5. Notice the error, then install visual studio community 2022 6. Re-run `PCbuild\build.bat -d -e` and see the same error I can't directly copy and paste between the VM and my host desktop but in this scenario, the error was that single line and I can use paste sites where necessary. Kind regards, Sam Ezeh On Sat, 2 Jul 2022 at 15:27, Sam Ezeh wrote: > > I have a Windows virtual machine and I'm following the instructions on > the devguide [1] to build Python inside it. > > When running `PCbuild\build\bat -e -d` I get "Cannot locate > MSBuild.exe on PATH or as MSBUILD variable". I've done a minimal > amount of searching [2][3] but I'm not well-acquainted with Windows > and don't understand the solutions. > > Thanks in advance. > > Kind regards, > Sam Ezeh > > [1]: https://devguide.python.org/compiler/ > [2]: https://bugs.python.org/issue41213 > [3]: https://bugs.python.org/issue33675 -- https://mail.python.org/mailman/listinfo/python-list
Building on Windows
I have a Windows virtual machine and I'm following the instructions on the devguide [1] to build Python inside it. When running `PCbuild\build\bat -e -d` I get "Cannot locate MSBuild.exe on PATH or as MSBUILD variable". I've done a minimal amount of searching [2][3] but I'm not well-acquainted with Windows and don't understand the solutions. Thanks in advance. Kind regards, Sam Ezeh [1]: https://devguide.python.org/compiler/ [2]: https://bugs.python.org/issue41213 [3]: https://bugs.python.org/issue33675 -- https://mail.python.org/mailman/listinfo/python-list
Re: Python installation
Inside my Windows virtual machine only entering `py` as the command brings up the repl, if that helps. Kind Regards, Sam Ezeh On Tue, 21 Jun 2022 at 18:15, Igor Korot wrote: > > Hi, > > On Tue, Jun 21, 2022 at 11:43 AM Brian Karinga wrote: > > > > Hello, > > > > I hope this email finds you well. > > > > I have been trying to download and install the latest version of python on > > my windows device. However, when I run the program, three options arise. > > These are: > > > > Modify > > Repair > > Uninstall > > > > I have executed the modify and repair options several times but nothing has > > changed. Please advise on what the problem could be and how it can be > > resolved. > > Is it possible that Python is already installed? > > Open "Command Prompt" window, type python and press "Enter". > > What do you see on the screen? > > Thank you. > > > > > I look forward to hearing from you. > > > > Thank you, > > Brian. > > -- > > https://mail.python.org/mailman/listinfo/python-list > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: Seeking deeper understanding of python equality (==)
Perhaps these source references are useful: Python/ceval.c (_PyEval_EvalFrameDefault) https://github.com/python/cpython/blob/main/Python/ceval.c#L3754-L3768 Objects/object.c (do_richcompare) https://github.com/python/cpython/blob/42fee931d055a3ef8ed31abe44603b9b2856e04d/Objects/object.c#L661-L713 Kind regards, Sam Ezeh On Fri, 6 May 2022 at 18:12, Jonathan Kaczynski wrote: > > Hi, > > I was recently trying to explain how python equality works and ran into a > gap in my knowledge. I haven't found any good pages going beneath a surface > level explanation of python equality comparison. > > I'll post my investigations below. What I think I'm looking for is where in > the source code (https://github.com/python/cpython) does the equality > comparison occur. I have an idea but wanted to ask first. > > > Using the dis module, we see the comparison operator is a single bytecode, > which is expected. > > ❯ docker run -it --rm ubuntu:jammy > root@919d94c98191:/# apt-get update > root@919d94c98191:/# apt-get --yes install python3 > root@919d94c98191:/# cat >play.py < import dis > import uuid > > def test(): > x = uuid.uuid4() > y = str(x) > x == y > return > > dis.dis(test) > EOF > root@f33b02fef026:/# python3 play.py > ... snip ... > 7 16 LOAD_FAST0 (x) > 18 LOAD_FAST1 (y) > 20 COMPARE_OP 2 (==) > 22 POP_TOP > ... snip ... > > > Stepping through the code with gdb, we see it jump from the compare > operator to the dunder-eq method on the UUID object. What I want to be able > to do is explain the in-between steps. Also, if you change `x == y` to `y > == x`, you still see the same behavior, which I assume has to do with > dunder-eq being defined on the UUID class and thus given priority. > > ❯ docker run -it --rm ubuntu:jammy > root@919d94c98191:/# apt-get update > root@919d94c98191:/# apt-get --yes install dpkg-source-gitarchive > root@919d94c98191:/# sed -i 's/^# deb-src/deb-src/' /etc/apt/sources.list > root@919d94c98191:/# apt-get update > root@919d94c98191:/# apt-get --yes install gdb python3.10-dbg > root@919d94c98191:/# apt-get source python3.10-dbg > root@919d94c98191:/# cat >play.py < import uuid > x = uuid.uuid4() > y = str(x) > breakpoint() > x == y > EOF > root@919d94c98191:/# gdb python3.10-dbg > (gdb) dir python3.10-3.10.4/Python > (gdb) run play.py > Starting program: /usr/bin/python3.10-dbg play.py > > warning: Error disabling address space randomization: Operation not > permitted > [Thread debugging using libthread_db enabled] > Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". > > //play.py(5)() > -> x == y > (Pdb) s > --Call-- > > /usr/lib/python3.10/uuid.py(239)__eq__() > -> def __eq__(self, other): > > > Thank you, > Jonathan > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Fwd: Do projects exist to audit PyPI-hosted packages?
-- Forwarded message - From: Sam Ezeh Date: Fri, 6 May 2022, 15:29 Subject: Re: Do projects exist to audit PyPI-hosted packages? To: Skip Montanaro I've had similar thoughts in the past. I don't know of anything but I wonder if repositiories for other languages might have something to deal with it. A related problem is that even if a package is maintained by somebody with good intentions, the account might be hijacked by a malicious actor and since PyPi is separate from source control, people might not be able to find out easily and malware could spread through PyPi. Kind regards, Sam Ezeh On Fri, 6 May 2022, 14:08 Skip Montanaro, wrote: > I woke with a start in what amounted to the middle of the night (I really > need to get about three more hours of sleep, but you'll understand why I > was awake to write this). > > Many years ago, so as to preserve my wrists, I wrote a tool > <https://github.com/smontanaro/python-bits/blob/main/src/watch.py> to > monitor mouse and keyboard activity. It tells me when to rest. I use it > when I have problems, then put it away until it's needed again. I have > resurrected it a few times over the years, most recently a month or two > ago. Having never been all that fond of how I tracked keyboard and mouse > activity, I was happy when I stumbled upon pynput > <https://pypi.org/project/pynput/>. "Yay!", I thought. My worries are > over. > > Then extremely early this morning I woke thinking, "Damn, this runs on my > computer and it can see my mouse and keyboard activity. How do I know it's > not stealing my keystrokes?" Not going back to sleep after that. So, I'm > going through the code (and the Xlib package on which it relies) to make > myself more comfortable that there are no issues. Note: I am *most > certainly not* accusing the pynput author of any mischief. In fact, I > suspect there's no problem with the package. It's got a bunch of stars and > plenty of forks on GitHub (for what that's worth). I suspect the code has > had plenty of eyeballs looking at it. Still, I don't really know how well > vetted it might be, so I have no assurances of that. I saw it mentioned > somewhere (discuss I think?), checked it out, and thought it would solve my > activity tracking in a cross-platform way. (I currently only use an Xorg > environment, so while I am looking at the code, I'm not paying attention to > the Windows or MacOS bits either.) > > This got me thinking. If I'm curious about pynput, might other people be as > well? What about other packages? I'm actually not worried about Python > proper or vulnerabilities which have already been found > <https://github.com/pypa/advisory-database>. PyPI currently advertises > that > it hosts over 373k packages. With that many hosted packages, it is almost > certainly a haven for some undetected vulnerabilities. Knowing which > packages have been audited — at least in a cursory fashion — could be used > as a further criterion to use when deciding which packages to consider > using on a project. > > So, does something already exist (pointers appreciated)? Thx... > > Skip > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
Re: Why no list as dict key?
Repeating the above points, here is an example of what would happen if
you tried. Dictionaries require their keys to be immutable as
under-the-hood they use hash tables and they'd fail when the
underlying values are allowed to change.
```
[sam@samtop]: ~>$ python
Python 3.10.2 (main, Jan 15 2022, 19:56:27) [GCC 11.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import functools
>>> import operator
>>> class HashableList(list):
... def __hash__(self):
... return functools.reduce(operator.xor, [key * value for
key, value in enumerate(self)], 5)
...
>>> x = HashableList([1,2,3])
>>> y = HashableList([1,2,3])
>>> dictionary = {x: 5}
>>> dictionary
{[1, 2, 3]: 5}
>>> dictionary[x]
5
>>> dictionary[y]
5
>>> x.append(4)
>>> dictionary
{[1, 2, 3, 4]: 5}
>>> dictionary[x]
Traceback (most recent call last):
File "", line 1, in
KeyError: [1, 2, 3, 4]
>>> dictionary[y]
Traceback (most recent call last):
File "", line 1, in
KeyError: [1, 2, 3]
>>>
```
On Wed, 20 Apr 2022 at 19:23, Abdur-Rahmaan Janhangeer
wrote:
>
> Greetings list,
>
> Using Python3.9, i cannot assign a list [1, 2] as key
> to a dictionary. Why is that so? Thanks in advanced!
>
> Kind Regards,
>
> Abdur-Rahmaan Janhangeer
> about
> github
> Mauritius
> --
> https://mail.python.org/mailman/listinfo/python-list
--
https://mail.python.org/mailman/listinfo/python-list
Re: Tuple unpacking inside lambda expressions
I went back to the code recently and I remembered what the problem was. I was using multiprocessing.Pool.pmap which takes a callable (the lambda here) so I wasn't able to use comprehensions or starmap Is there anything for situations like these? Kind Regards, Sam Ezeh On Sat, 16 Apr 2022 at 22:36, Sam Ezeh wrote: > > Two questions here. > > Firstly, does anybody know of existing discussions (e.g. on here or on > python-ideas) relating to unpacking inside lambda expressions? > > I found myself wanting to write the following. > > ``` > map( > lambda (module, data): result.process(module, data), > jobs > ) > ``` > However, it's of course not legal Python syntax. > > The following were potential options but I felt they removed some of > the meaning from the code, making it less understandable for other > people. > > ``` > map( > lambda job: result.process(job[0], job[1]), > jobs > ) > ``` > > ``` > map( > lambda job: result.process(*job), > jobs > ) > ``` > > Secondly, for situations like these, do you have any go-to methods of > rewriting these while maintaining clarity? > > Kind Regards, > Sam Ezeh -- https://mail.python.org/mailman/listinfo/python-list
Re: Tuple unpacking inside lambda expressions
This also works great! Kind Regards, Sam Ezeh On Tue, 19 Apr 2022 at 12:03, Antoon Pardon wrote: > > Op 16/04/2022 om 23:36 schreef Sam Ezeh: > > Two questions here. > > > > Firstly, does anybody know of existing discussions (e.g. on here or on > > python-ideas) relating to unpacking inside lambda expressions? > > > > I found myself wanting to write the following. > > > > ``` > > map( > > lambda (module, data): result.process(module, data), > > jobs > > ) > > ``` > > However, it's of course not legal Python syntax. > > Why not write: > > itertools.starmap(result.process, jobs) > > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Enums and nested classes
Hello everyone, Has anyone here used or attempted to use a nested class inside an enum? If so, how did you find it? (what did you expect to happen and did your expectations align with resulting behaviour etc.) Here are two examples describing the situation I'm talking about ``` class Outer(Enum): a = 1 b = 2 class Inner(Enum): foo = 10 bar = 11 ``` ``` class Outer(Enum): a = 1 b = 2 class Inner: c = None def __init__(self): ``` Kind Regards, Sam Ezeh -- https://mail.python.org/mailman/listinfo/python-list
Re: Proposal: Syntax for attribute initialisation in __init__ methods
I'll see if I can find out how positional only and keyword only arguments are used in __init__ methods in the wild and I'll see if there have been any other discussions talking about what this approach could offer. On Sun, 17 Apr 2022 at 02:54, dn wrote: > > On 17/04/2022 09.20, Sam Ezeh wrote: > >> Perhaps I'm missing the point, but what functionality or advantage(s) > >> does this give, over data-classes? > > > > One advantage is maintaining control over the __init__ function without > > having to write extra code to do so. In the linked discussion from > > python-ideas, it was mentioned that keyword-only and positional-only > > arguments can't be used with dataclasses [1]. > > > >> Maybe Dataclasses are not being used as much as one might hope, but they > >> are relatively new, and many Python-Masters simply carry-on constructing > >> classes the way they have for years... > > > > I think one concern I have is that even if this is useful, it might > > still fall to the same fate. > > > Don't be discouraged by that - and that thread was not the first of such > discussions! The way Python is being applied is continually changing... > > I'm not sure about the criticism of dataclasses though. Starting with > 'explicit over implicit', once a parameter-list is more than two or > three long, shouldn't we be using 'labels' in order to avoid (potential) > confusion, ie keyword-parameters? > > This removes the order/sequence of arguments from the list of potential > problems/gotchas one can fall into! > > In which case, I'm wondering just how often the criticism applies 'in > real life'? > > So, now the question becomes: what are the cases/examples which > require/desire improvement over the 'traditional' __init__ of > attributes, and facilities offered through dataclasses? > -- > Regards, > =dn > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: Tuple unpacking inside lambda expressions
> In general, if you're using map() with a lambda function, it's often simpler to switch to a comprehension. Oh, of course, completely went past my head. > [result.process(module, data) for module, data in jobs] And this works great, thanks! On Sat, 16 Apr 2022 at 22:42, Chris Angelico wrote: > > On Sun, 17 Apr 2022 at 07:37, Sam Ezeh wrote: > > > > Two questions here. > > > > Firstly, does anybody know of existing discussions (e.g. on here or on > > python-ideas) relating to unpacking inside lambda expressions? > > > > I found myself wanting to write the following. > > > > ``` > > map( > > lambda (module, data): result.process(module, data), > > jobs > > ) > > ``` > > However, it's of course not legal Python syntax. > > What about: > > [result.process(module, data) for module, data in jobs] > > (or with () instead of [] around the outside if you want a generator)? > > In general, if you're using map() with a lambda function, it's often > simpler to switch to a comprehension. > > ChrisA > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Fwd: Proposal: Syntax for attribute initialisation in __init__ methods
I've just seen Pablo's very recent post on python-ideas so I thought I'd link it here. [1] [1]: https://mail.python.org/archives/list/python-id...@python.org/message/SCXHEWCHBJN3A7DPGGPPFLSTMBLLAOTX/ Kind Regards, Sam Ezeh On Fri, 15 Apr 2022 at 22:57, Ethan Furman wrote: > > On 4/15/22 04:19, Sam Ezeh wrote: > > Elsewhere, the idea of supporting new syntax to automatically initialise > > attributes provided as arguments to __init__ methods was raised. > > [...] > > Good post! You'll want to send this to python-ideas at some point (that's > where most new python features are > discussed). This particular desire has come up in the past, so you'll need > to do some more research (i.e. find the > previous threads on python-ideas) so you can answer objections already > raised, or find new data supporting/refuting > previous arguments. > > -- > ~Ethan~ > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Fwd: Proposal: Syntax for attribute initialisation in __init__ methods
> Perhaps I'm missing the point, but what functionality or advantage(s) > does this give, over data-classes? One advantage is maintaining control over the __init__ function without having to write extra code to do so. In the linked discussion from python-ideas, it was mentioned that keyword-only and positional-only arguments can't be used with dataclasses [1]. > Maybe Dataclasses are not being used as much as one might hope, but they > are relatively new, and many Python-Masters simply carry-on constructing > classes the way they have for years... I think one concern I have is that even if this is useful, it might still fall to the same fate. [1]: https://mail.python.org/archives/list/python-id...@python.org/message/SCTXSEKOWDRDGVXXOEB7JUC6WE7XKGMO/ On Fri, 15 Apr 2022 at 22:30, dn wrote: > > On 15/04/2022 23.19, Sam Ezeh wrote: > ... > > Kudos for doing the research! > > > > Some related implementations are attrs, dataclasses and the use of a > > decorator. And there's potentially a point to be raised that the results > > from the first query indicate that the @dataclasse decorator is not being > > used enough. One advantage this proposal offers is control over the > > arguments that the __init__ function takes. > > > > A downside to using a decorator is that it might become difficult to accept > > arguments that don't need to be assigned to anything. > > > > I gave the example of the following code (unlike the above, this is not > > taken from existing python source code). In this example, a decorator can't > > assign all of the arguments to attributes or else it would produce code > > that does something different. > ... > > > I will support anything which reduces 'boiler-plate' or 'make busy' work! > > Perhaps I'm missing the point, but what functionality or advantage(s) > does this give, over data-classes? > > Maybe Dataclasses are not being used as much as one might hope, but they > are relatively new, and many Python-Masters simply carry-on constructing > classes the way they have for years... > > If data-classes give the impression of being 'syntactic sugar', there's > no particular need to use them - and certainly no rule or demand. > > There are constructs where one might find it easier not to use them. > > @dataclass does allow init=False. > > There is an argument which says that all data-attributes should be > 'created' inside an __init__() or __post_init__(), rather than > 'somewhere', 'later'. > -- > Regards, > =dn > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Tuple unpacking inside lambda expressions
Two questions here. Firstly, does anybody know of existing discussions (e.g. on here or on python-ideas) relating to unpacking inside lambda expressions? I found myself wanting to write the following. ``` map( lambda (module, data): result.process(module, data), jobs ) ``` However, it's of course not legal Python syntax. The following were potential options but I felt they removed some of the meaning from the code, making it less understandable for other people. ``` map( lambda job: result.process(job[0], job[1]), jobs ) ``` ``` map( lambda job: result.process(*job), jobs ) ``` Secondly, for situations like these, do you have any go-to methods of rewriting these while maintaining clarity? Kind Regards, Sam Ezeh -- https://mail.python.org/mailman/listinfo/python-list
Proposal: Syntax for attribute initialisation in __init__ methods
f when an __init__ method only contains arguments that will become attributes. From the cryptography library, there's the following example. ``` class _DeprecatedValue: def __init__(self, value: object, message: str, warning_class): self.value = value self.message = message self.warning_class = warning_class ``` With the new syntax, this would become the following ``` class _DeprecatedValue: def __init__(self, @value: object, @message: str, @warning_class): pass ``` The empty __init__ method seems unnecessary so perhaps it could be reduced further to the following ``` class _DeprecatedValue: @value: object @message: str @warning_class ``` With regards to implementation details, there are questions about the order of execution, right now it seems to make sense to me that attributes should be assigned to prevent them from being overridden by any calls to super() for code similar to that in the numpy example. Another question could be what happens if the syntax is used outside of an __init__ method. Right now, it seems to me that this could be ok and the code could run the same as it would inside the __init__ method. There is also the question of what happens if the syntax is used inside a function that isn't defined in a class, and perhaps this usage should be rejected. As another edge case, there's the question of what would happen if this syntax is used on functions labelled with the @staticmethod decorator. Type hinting will also have to be dealt with. With all of this in mind, I'd like to hear what other people think about this proposal. To perform the queries I created a tool called presearch which others might find useful. I found it quite fun to make however it's only been in existence for 2 days so there currently isn't any documentation and it's lacking in several areas. The source code can be found here: https://github.com/dignissimus/presearch Kind Regards, Sam Ezeh -- https://mail.python.org/mailman/listinfo/python-list
Re: Functionality like local static in C
I've seen people use function attributes for this. ``` Python 3.10.2 (main, Jan 15 2022, 19:56:27) [GCC 11.1.0] on linux Type "help", "copyright", "credits" or "license" for more information. >>> def function(): ... print(function.variable) ... function.variable += 1 ... >>> function.variable = 1 >>> function() 1 >>> function() 2 >>> ``` If necessary, the variable can be initialised inside the function too. Kind Regards, Sam Ezeh On Thu, 14 Apr 2022 at 16:36, Sam Ezeh wrote: > > I've seen people use function attributes for this. > ``` > Python 3.10.2 (main, Jan 15 2022, 19:56:27) [GCC 11.1.0] on linux > Type "help", "copyright", "credits" or "license" for more information. > >>> def function(): > ... print(function.variable) > ... function.variable += 1 > ... > >>> function.variable = 1 > >>> function() > 1 > >>> function() > 2 > >>> > ``` > > If necessary, the variable can be initialised inside the function too. > > Kind Regards, > Sam Ezeh > > > On Thu, 14 Apr 2022 at 16:26, Cecil Westerhof via Python-list > wrote: > > > > In C when you declare a variable static in a function, the variable > > retains its value between function calls. > > The first time the function is called it has the default value (0 for > > an int). > > But when the function changes the value in a call (for example to 43), > > the next time the function is called the variable does not have the > > default value, but the value it had when the function returned. > > Does python has something like that? > > > > -- > > Cecil Westerhof > > Senior Software Engineer > > LinkedIn: http://www.linkedin.com/in/cecilwesterhof > > -- > > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
