Mailman 3 June 2018 - Python-ideas

Allow callable in slices
by Michel Desmoulin June 9, 2018

June 9, 2018

Given 2 callables checking when a condition arises and returning True: def starting_when(element): ... def ending_when(element: ... Allow: a_list[starting_when:] To be equivalent to: from itertools import dropwhile list(dropwhile(lambda x: not starting_when(x), a_list)) And: a_list[:ending_when] To: from itertools import takewhile list(takewhile(lambda x: not ending_when(x), a_list))

2 1

Re: [Python-ideas] Trigonometry in degrees
by Adam Bartoš June 9, 2018

June 9, 2018

Steven D'Arpano wrote: > On Fri, Jun 08, 2018 at 11:11:09PM +0200, Adam Bartoš wrote: > >>* But if there are both sin and dsin, and you ask about the difference *>>* between them, the obvious answer would be that one takes radians and the *>>* other takes degrees. The point that the degrees version is additionally *>>* exact on special values is an extra benefit. *> > No, that's not an extra benefit, it is the only benefit! > > If we can't make it … [View More]

2 1

Allow callables in slices
by Michel Desmoulin June 9, 2018

June 9, 2018

Such as that: def starting_when(element): ... a_list[starting_when:] Is equivalent to: from itertools import dropwhile def starting_when(element): ... list(dropwhile(lambda x: not starting_when(x), a_list)) And def ending_when(element: ... a_list[:ending_when] To: from itertools import dropwhile def ending_when(element: ... list(itertools.takwhile(lambda x: not condition(x), a_list))

3 3

Re: [Python-ideas] A PEP on introducing variables on 'if' and 'while'
by Jeroen Demeyer June 9, 2018

June 9, 2018

On 2018-06-09 14:43, Juancarlo Añez wrote: > Is there a guide about writing (and publishing) PEPs? https://www.python.org/dev/peps/pep-0001/

1 0

__dir__ in which folder is this py file
by Yuval Greenfield June 9, 2018

June 9, 2018

Hi Ideas, I often need to reference a script's current directory. I end up writing: import os SRC_DIR = os.path.dirname(__file__) But I would prefer to have a new dunder for that. I propose: "__dir__". I was wondering if others would find it convenient to include such a shortcut. Here are some examples of dirname(__file__) in prominent projects. https://github.com/tensorflow/models/search?l=Python&q=dirname&type= https://github.com/django/django/search?l=Python&q=dirname&… [View More]

20 41

Re: [Python-ideas] Making Path() a built in.
by Michel Desmoulin June 9, 2018

June 9, 2018

Creating built in dynamically is not a good idea. Tools complain, new comers wonder where it comes from, it sets a precedent for adding more or debating about it. Better have the debate once here, make it official or decline it officially, and have a clean result. Le 08/06/2018 à 21:28, Barry a écrit : > I think you forgot to to reply to the list. > Barry > > >> On 8 Jun 2018, at 13:16, Michel Desmoulin <desmoulinmichel(a)gmail.com> wrote: >> >> … [View More]

1 0

Fwd: New suggested built in keyword: do
by Randy Diaz June 8, 2018

June 8, 2018

I think that the keyword do would solve problems that occur when people want a simple way to run a command over an iterable but they dont want to store the data. example: do print(x) for x in range(50) --------- this above command will not return anything and will just run the command that is underlined over a generator. thus running a command comprehension or do comprehension. this will stop people from using the list comprehension to run an iterable through a function when they dont … [View More]

9 8

Re: [Python-ideas] Trigonometry in degrees
by Adam Bartoš June 8, 2018

June 8, 2018

Steven D'Aprano wrote: > On Fri, Jun 08, 2018 at 10:53:34AM +0200, Adam Bartoš wrote: >> Wouldn't sin(45 * DEG) where DEG = 2 * math.pi / 360 be better that >> sind(45)? This way we woudn't have to introduce new functions. (The problem >> with nonexact results for nice angles is a separate issue.) > > But that's not a separate issue, that's precisely one of the motives for > having dedicated trig functions for degrees. > > sind(45) (or dsin(45), as I would … [View More]

3 2

Allow popping of slices
by Ben Rudiak-Gould June 8, 2018

June 8, 2018

The `pop` method of built-in sequences is basically an atomic version of val = self[pos] del self[pos] return val If this behavior was extended to the case where `pos` is a slice, you could write things like: def cut_deck(deck, pos): deck.extend(deck.pop(slice(0, pos))) def bfs(roots): depth, frontier = 0, list(roots) while frontier: depth += 1 for item in frontier.pop(slice(None)): ... … [View More]

3 3

Add dict.append and dict.extend
by Ben Rudiak-Gould June 8, 2018

June 8, 2018

I'd like to propose adding `append` and `extend` methods to dicts which behave like `__setitem__` and `update` respectively, except that they raise an exception (KeyError?) instead of overwriting preexisting entries. Very often I expect that the key I'm adding to a dict isn't already in it. If I want to verify that, I have to expand my single-line assignment statement to 3-5 lines (depending on whether the dict and key are expressions that I now need to assign to local variables). If I don't … [View More]

8 8