date:20170106

Re: The hardest problem in computer science...

2017-01-06 Thread Steve D'Aprano

On Sat, 7 Jan 2017 12:03 am, Steve D'Aprano wrote:

> The second hardest problem in computer science is cache invalidation.
> 
> The *hardest* problem is naming things.

Thanks everyone who answered, but I think some of you misunderstood my
question. I know that the individual characters themselves are called some
variation of "line drawing characters", or "box drawing characters". But
the important part of the question was given by the Python code:

> XXX = namedtuple("XXX", "vline tee corner")
> 
> default_YYY = XXX("│  ", "├─ ", "└─ ")
> bold_YYY = XXX("┃  ", "┣━ ", "┗━ ")
> ascii_YYY = XXX("|  ", "|- ", "+- ")
> 
> def draw_tree(tree, YYY=default_YYY):
> ...
> 
> 
> but what do I call XXX and YYY?

After puzzling over this for three days, it suddenly hit me:

Theme = namedtuple("Theme", "vline tee corner")

DEFAULT = Theme("│  ", "├─ ", "└─ ")
BOLD = Theme("┃  ", "┣━ ", "┗━ ")
ASCII = Theme("|  ", "|- ", "+- ")

def draw_tree(tree, theme=DEFAULT):
...

Ethan's idea of "style" is also good.

Thanks for all your ideas!

-- 
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.

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Re: Search a sequence for its minimum and stop as soon as the lowest possible value is found

2017-01-06 Thread Rustom Mody

On Saturday, January 7, 2017 at 12:26:04 PM UTC+5:30, Jussi Piitulainen wrote:
> Paul Rubin writes:
> 
> > Peter Otten writes:
> >> How would you implement stopmin()?
> >
> > Use itertools.takewhile
> 
> How? It consumes the crucial stop element:
> 
>it = iter('what?')
>list(takewhile(str.isalpha, it)) # ==> ['w', 'h', 'a', 't']
>next(it, 42) # ==> 42

I was also wondering how…
In a lazy language (eg haskell) with non-strict foldr (reduce but rightwards)
supplied non-strict operator this is trivial.
ie in python idiom with reduce being right_reduce
reduce(operator.mul, [1,2,0,4,...], 1)
the reduction would stop at the 0
Not sure how to simulate this in a strict language like python
Making fold(r) non-strict by using generators is ok
How to pass a non-strict operator?
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Re: Search a sequence for its minimum and stop as soon as the lowest possible value is found

2017-01-06 Thread Jussi Piitulainen

Paul Rubin writes:

> Peter Otten writes:
>> How would you implement stopmin()?
>
> Use itertools.takewhile

How? It consumes the crucial stop element:

   it = iter('what?')
   list(takewhile(str.isalpha, it)) # ==> ['w', 'h', 'a', 't']
   next(it, 42) # ==> 42
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RE: Namedtuples: TypeError: 'str' object is not callable

2017-01-06 Thread Deborah Swanson

Chris Angelico wrote, on January 06, 2017 9:14 PM
> 
> On Sat, Jan 7, 2017 at 4:07 PM, Deborah Swanson 
>  wrote:
> >
> > I really don't know how long it would've taken me to think of that,
so 
> > thank you!
> 
> I have a well-trained crystal ball :)
> 
> ChrisA

More like a very experienced eye. I keep hoping I'll get one of those,
but it takes time.

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Re: Namedtuples: TypeError: 'str' object is not callable

2017-01-06 Thread Chris Angelico

On Sat, Jan 7, 2017 at 4:07 PM, Deborah Swanson
 wrote:
> And you would be precisely correct. I have a variable named 'map', and I
> intended to delete it and the code that used it, but totally forgot
> about it. It's still in there somewhere, but a simple search will find
> it.
>
> I really don't know how long it would've taken me to think of that, so
> thank you!

I have a well-trained crystal ball :)

ChrisA
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RE: Namedtuples: TypeError: 'str' object is not callable

2017-01-06 Thread Deborah Swanson

Chris Angelico wrote, on January 06, 2017 8:05 PM
> To: python-list@python.org
> Subject: Re: Namedtuples: TypeError: 'str' object is not callable
> 
> 
> On Sat, Jan 7, 2017 at 2:46 PM, Deborah Swanson 
>  wrote:
> > And here's the Traceback in PyCharm:
> >   File "E:/Coding projects/Pycharm/Moving/moving_numberedtuples.py",
> > line 139, in moving()
> > for lst in map(listings._make, csv.reader(open('E:\\Coding 
> > projects\\Pycharm\\Moving\\Moving 2017 in.csv',"r"))):
> > TypeError: 'str' object is not callable
> >
> > What str object is not callable, and how do I fix it?
> 
> Toss in a 'print' above that. You're calling map and open 
> (and csv.reader, but I doubt you've shadowed that). My money 
> would be on 'map' having been assigned something.
> 
> ChrisA

And you would be precisely correct. I have a variable named 'map', and I
intended to delete it and the code that used it, but totally forgot
about it. It's still in there somewhere, but a simple search will find
it.

I really don't know how long it would've taken me to think of that, so
thank you!

Deborah

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Re: Namedtuples: TypeError: 'str' object is not callable

2017-01-06 Thread Chris Angelico

On Sat, Jan 7, 2017 at 2:46 PM, Deborah Swanson
 wrote:
> And here's the Traceback in PyCharm:
>   File "E:/Coding projects/Pycharm/Moving/moving_numberedtuples.py",
> line 139, in moving()
> for lst in map(listings._make, csv.reader(open('E:\\Coding
> projects\\Pycharm\\Moving\\Moving 2017 in.csv',"r"))):
> TypeError: 'str' object is not callable
>
> What str object is not callable, and how do I fix it?

Toss in a 'print' above that. You're calling map and open (and
csv.reader, but I doubt you've shadowed that). My money would be on
'map' having been assigned something.

ChrisA
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Namedtuples: TypeError: 'str' object is not callable

2017-01-06 Thread Deborah Swanson

I'm not sure what Python is complaining about here, or why.
 
Here's the example from the Python docs: 
https://docs.python.org/3/library/collections.html#collections.namedtupl
e

EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title,
department, paygrade')

import csv
for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv",
"rb"))):
print(emp.name, emp.title)

And here's my code:

listings = namedtuple('listings', ['CLDesc', 'url', 'desc',
'Description',  'Location', 'STco', 'miles', 'Kind', 'Rent', 'Date',
'br', 'Notes', 
'yesno', 'mark', 'arc'])
for lst in map(listings._make, csv.reader(open('Moving 2017.csv',
"r"))):
.
.

(['x', 'y'] is a valid format for the field names, and there are no
errors when the definition for listings executes.)


And here's the Traceback in PyCharm:
  File "E:/Coding projects/Pycharm/Moving/moving_numberedtuples.py",
line 139, in moving()
for lst in map(listings._make, csv.reader(open('E:\\Coding
projects\\Pycharm\\Moving\\Moving 2017 in.csv',"r"))):
TypeError: 'str' object is not callable

What str object is not callable, and how do I fix it?  I see an
iteration variable (lst), a namedtuples method call(listings._make,
which makes a new instance of listings) and a csv.reader call, a
variable and 2 method calls, none of which are bare strings, except
possibly 'listings._make', but there's no str it might be trying to call
that I can see. My 'for' statement looks like a good copy of the example
from the docs to me, and the example in the docs uses
'EmployeeRecord._make' with no parentheses.

Is the example from the docs possibly in error? I don't see any other
possibility, but maybe I'm not looking in the right place. 

I don't know enough about classes in Python yet to know if this is ok or
not. And when I tried again with 'listings._make()', I got:

TypeError: _make() missing 1 required positional argument: 'iterable'.

This suggests that maybe 'listings._make' is wrong, but if it should be
'listings._make()', what should the iterable be? 'listings'?

'listings._make(listings)' looks awfully redundant for Python, so 
'_make(listings)' would make more sense (pun not intended), and seems to
be what the error thinks it is. But when I change it to
'_make(listings)', I get:

NameError: name '_make' is not defined

'listings._make(listings)' gets "TypeError: 'type' object is not
iterable", which answers the question of whether a namedtuple instance
(if that's what 'listings' is) is an iterable. It isn't.

There might be a version problem here. I'm using Python 3.4.3, and the
url for this page simply indicates version 3. As most of us know,
there's a lot of variance between dot versions of 3, and quite possibly
not all of the changes are documented correctly. In 3.4.3 the usage
might be slightly different, or the code broken.

Any help with this would be hugely appreciated.


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Re: The hardest problem in computer science...

2017-01-06 Thread Larry Hudson via Python-list

On 01/06/2017 05:03 AM, Steve D'Aprano wrote:

The second hardest problem in computer science is cache invalidation.

The *hardest* problem is naming things.

In a hierarchical tree view widget that displays items like this:

Fiction
├─ Fantasy
│ ├─ Terry Pratchett
│ │ ├─ Discworld

[snip]

but what do I call XXX and YYY?

Seriously-considering-just-hard-coding-them-as-magic-constants-ly y'rs,

I don't know if this is helpful or even relevant, but here is a class for using these
box-drawing characters that I wrote for my own use. (I'm just a hobby programmer...)
It's not very elegant and not particularly convenient to use, but it is usable. And I hesitate
to post it because it is so long (approx 90 line docstring to explain its use, and ending with
some test code). In any case, here it is...

# boxch.py

"""
BoxChr class to handle box-drawing characters.

The character is selected by a two-character string:
'tl', 'tm', 'tr' -- Top Left, Top Mid, Top Right: ┌ ┬ ┐
'ml', 'mm', 'mr' -- Mid Left, Mid Mid, Mid Right: ├ ┼ ┤
'bl', 'bm', 'br' -- Bot Left, Bot Mid, Bot Right: └ ┴ ┘
'hz', 'vt' -- Horizontal and Vertical lines: ─ │
Case is ignored. Invalid selection string returns a dot: '·'
NOTE: It is currently disabled, but the code is still
available to handle small and large dots with 'dt' and 'dd'.
These both ignore the style.

The style is selected by a two-character string:
The characters are 's', 'd' and 'b' for single, double and bold.
The first character defines the horizontal components,
the second defines the vertical components.
The valid styles are 'ss', 'sd', 'sb', 'ds', 'dd', 'bs', 'bb'.
The potential styles 'db' and 'bd' are invalid.
The class defaults to 'ss' -- single horizontal, single vertical.
Case is ignored. Invalid style string raises ValueError.

NOTE: The following examples assume bc has been set to a BoxChr class.
bc = BoxChr() # Style defaults to 'ss'
or
bc = BoxChr('sd') # Style set to single/double, or whatever desired.
(Examples assume 'ss' style.)

Attributes:
style: set or return the style-code string.
Case is ignored. Invalid style raises ValueError.
Examples: bc.style = 'ds' -- sets style to double/single.
st = bc.style -- sets variable st to current style code.

Methods:
[] (__getitem__): Returns selected box character.
Case is ignored. Invalid selector returns a dot: '·'
Example: bc['tm'] returns '┬'

bxstr(): Returns a string created from a sequence of box character codes
and 'normal' characters. (in this description 'selector' refers
to the two-character codes as defined above.)

Each element of the given sequence (list or tuple) must be a
string, either a series of selector codes, or a 'normal' string
(one without any box selectors). The box character selector string
must start with 'BX' followed by the selector codes, separated by
spaces. The 'BX' must be upper case, but the case of the selector
codes is ignored. A space between the 'BX' prefix and the first
selector code is optional. This selector string can only contain
selector codes. 'Normal' characters are simply given as normal
strings, interspersed with the selector strings in the given
sequence.

If the selection is only box characters, it can opionally be passed
as a single string rather than enclosing it in a list.
Example:
seq = ['BX ml hz', ' TEXT ', 'BX hz mr']
bc.bxstr(seq) returns '├─ TEXT ─┤'
Note:
If you need a string beginning with 'BX' it has to be given
as a single-character string 'B' followed by a string containing
the remaining text. Example 'BX etc' must be given as:
['B', 'X etc'].

boxtext(): Create boxed text, returned as a single string with
embedded newlines.

Parameters:
txt The text to use
tsize Expand tabs to specified number of spaces, Default is 4
just'<', '^' or '>' as left/center/right justification.
Default is '<' — left-justified.
tallIf True, inserts a blank line above and below the text.
If False, no extra blank lines are used.
Default is True.

Text can be either a single string with embedded newlines (ie. a
triple-quoted string) or list of strings. Trailing blank lines
are removed. Center and right justification will strip whitespace
from both ends of the lines. Left justification (the default)
only strips trailing whitespace.

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