Mailman 3 March 2017 - Python-ideas

@classproperty, @abc.abstractclasspropery, etc.
by K. Richard Pixley Dec. 16, 2020

Dec. 16, 2020

There's a whole matrix of these and I'm wondering why the matrix is currently sparse rather than implementing them all. Or rather, why we can't stack them as: class foo(object): @classmethod @property def bar(cls, ...): ... Essentially the permutation are, I think: {'unadorned'|abc.abstract}{'normal'|static|class}{method|property|non-callable attribute}. concreteness implicit first arg type name comments {unadorned} {unadorned} method def foo(): exists … [View More]now {unadorned} {unadorned} property @property exists now {unadorned} {unadorned} non-callable attribute x = 2 exists now {unadorned} static method @staticmethod exists now {unadorned} static property @staticproperty proposing {unadorned} static non-callable attribute {degenerate case - variables don't have arguments} unnecessary {unadorned} class method @classmethod exists now {unadorned} class property @classproperty or @classmethod;@property proposing {unadorned} class non-callable attribute {degenerate case - variables don't have arguments} unnecessary abc.abstract {unadorned} method @abc.abstractmethod exists now abc.abstract {unadorned} property @abc.abstractproperty exists now abc.abstract {unadorned} non-callable attribute @abc.abstractattribute or @abc.abstract;@attribute proposing abc.abstract static method @abc.abstractstaticmethod exists now abc.abstract static property @abc.staticproperty proposing abc.abstract static non-callable attribute {degenerate case - variables don't have arguments} unnecessary abc.abstract class method @abc.abstractclassmethod exists now abc.abstract class property @abc.abstractclassproperty proposing abc.abstract class non-callable attribute {degenerate case - variables don't have arguments} unnecessary I think the meanings of the new ones are pretty straightforward, but in case they are not... @staticproperty - like @property only without an implicit first argument. Allows the property to be called directly from the class without requiring a throw-away instance. @classproperty - like @property, only the implicit first argument to the method is the class. Allows the property to be called directly from the class without requiring a throw-away instance. @abc.abstractattribute - a simple, non-callable variable that must be overridden in subclasses @abc.abstractstaticproperty - like @abc.abstractproperty only for @staticproperty @abc.abstractclassproperty - like @abc.abstractproperty only for @classproperty --rich [View Less]

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Specify number of items to allocate for array.array() constructor
by Sven Rahmann Feb. 22, 2020

Feb. 22, 2020

At the moment, the array module of the standard library allows to create arrays of different numeric types and to initialize them from an iterable (eg, another array). What's missing is the possiblity to specify the final size of the array (number of items), especially for large arrays. I'm thinking of suffix arrays (a text indexing data structure) for large texts, eg the human genome and its reverse complement (about 6 billion characters from the alphabet ACGT). The suffix array is a long int … [View More]

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Positional-only parameters
by Victor Stinner Sept. 11, 2018

Sept. 11, 2018

Hi, For technical reasons, many functions of the Python standard libraries implemented in C have positional-only parameters. Example: ------- $ ./python Python 3.7.0a0 (default, Feb 25 2017, 04:30:32) >>> help(str.replace) replace(self, old, new, count=-1, /) # <== notice "/" at the end ... >>> "a".replace("x", "y") # ok 'a' >>> "a".replace(old="x", new="y") # ERR! TypeError: replace() takes at least 2 arguments (0 given) ------- When converting the … [View More]

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Implicit string literal concatenation considered harmful?
by Guido van Rossum March 14, 2018

March 14, 2018

I just spent a few minutes staring at a bug caused by a missing comma -- I got a mysterious argument count error because instead of foo('a', 'b') I had written foo('a' 'b'). This is a fairly common mistake, and IIRC at Google we even had a lint rule against this (there was also a Python dialect used for some specific purpose where this was explicitly forbidden). Now, with modern compiler technology, we can (and in fact do) evaluate compile-time string literal concatenation with the '+' … [View More]

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dict(default=int)
by Steven Piantadosi May 30, 2017

May 30, 2017

Hi All, I find importing defaultdict from collections to be clunky and it seems like having a default should just be an optional keyword to dict. Thus, something like, d = dict(default=int) would be the same as from collections import defaultdict d = defaultdict(int) Any thoughts? Thanks, ++Steve

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Proposal: making __str__ count in time's class
by Francesco Franchina April 9, 2017

April 9, 2017

Hello everyone, I'm shortly writing to you about a reflection I lately made upon the current functioning of __str__ for the time's class. Before expressing my thought and proposal, I want to make sure we all agree on a simple and clear fact: the __str__ magic method is used to give a literal and human-readable representation to the object (unlike __repr__). Generally this is true across the python panorama. It's not true for the time class, for example. *>>> import time>>&… [View More]

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What about regexp string litterals : re".*" ?
by Simon D. April 3, 2017

April 3, 2017

Hello, After some french discussions about this idea, I subscribed here to suggest adding a new string litteral, for regexp, inspired by other types like : u"", r"", b"", br"", f""… The regexp string litteral could be represented by : re"" It would ease the use of regexps in Python, allowing to have some regexp litterals, like in Perl or JavaScript. We may end up with an integration like : >>> import re >>> if re".k" in 'ok': ... print "ok" ok >>> … [View More]

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Construct a matrix from a list: matrix multiplication
by Chris Angelico April 1, 2017

April 1, 2017

This keeps on coming up in one form or another - either someone multiplies a list of lists and ends up surprised that they're all the same, or is frustrated with the verbosity of the alternatives. Can we use the matmul operator for this? class List(list): def __matmul__(self, other): return [copy.copy(x) for x in self for _ in range(other)] >>> x = List([[0]*4]) @ 2 >>> x [[0, 0, 0, 0], [0, 0, 0, 0]] >>> x[0][0] = 1 >>> x [[1, 0, 0, 0], [0, 0, … [View More]

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Re: [Python-ideas] unify usage of mutable and immutable objects
by 语言破碎处 April 1, 2017

April 1, 2017

> To me, 'pop' implies mutation. Tuples do not have a pop method, and it > is not obvious to me that either tuples or frozensets should. What are > the use cases that are not better served by converting to list or set? > -- > Terry Jan Reedy 1) coverting to set or list is O(n) in time 2) if I have to keep the old copy, standard set solution will be O(n) both in time and space! working examples: 1) priority queue: insert and pop occur 2) share immutable data … [View More]

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Way to repeat other than "for _ in range(x)"
by Markus Meskanen March 31, 2017

March 31, 2017

Hi Pythonistas, yet again today I ended up writing: d = [[0] * 5 for _ in range(10)] And wondered, why don't we have a way to repeat other than looping over range() and using a dummy variable? This seems like a rather common thing to do, and while the benefit doesn't seem much, something like this would be much prettier and more pythonic than using underscore variable: d = [[0] * 5 repeat_for 10] And could obviously be used outside of comprehensions too: repeat_for 3: print('… [View More]

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