Mailman 3 February 2021 - Python-ideas

Arrow functions polyfill
by Paul Sokolovsky March 11, 2021

March 11, 2021

Hello, On Fri, 12 Feb 2021 18:26:53 +1100 Chris Angelico <rosuav(a)gmail.com> wrote: > On Fri, Feb 12, 2021 Paul Sokolovsky <pmiscml(a)gmail.com> wrote: > > ... And on the 2nd thought, that won't work. The reason it works in > > JS is that it doesn't have tuples. In Python, "(a, b) => (1, 2)" > > means "compare a tuple for greater-or-equal". > > Should be safe actually - "=>" is not a valid comparison operator. To punish myself for making such … [View More]stupid mistakes, I volunteered to implement PoC of that. And by long honorable tradition, improvements to Python get implemented in Python first. So with my "imphook" thingy https://pypi.org/project/imphook/, and with the hook module at the end, following works as expected: =========== $ cat example_arrow_func.py f = (a, b) => a + b print(f(1, 2)) res = ((a, b) => a + b)(3, 4) print(res) print(list(map((x) => x * 2, [1, 2, 3, 4]))) # Confirm there's no crashing on bare tuple at the tail of file. (1, 2) $ python3 -m imphook -i mod_arrow_func -m example_arrow_func 3 7 [2, 4, 6, 8] =========== The implementation was written a bit cowboyishly in 15 mins, maybe, just maybe, you can still crash it. (For example, it clearly doesn't support newlines in arrow param list): ===== mod_arrow_func.py ====== import sys import tokenize import imphook class TokBuf: def __init__(self): self.tokens = [] def append(self, t): self.tokens.append(t) def clear(self): self.tokens.clear() def empty(self): return not self.tokens def spool(self): yield from self.tokens self.clear() def xform(token_stream): tokbuf = TokBuf() for t in token_stream: if t[1] == "(": # We're interested only in the deepest parens. if not tokbuf.empty(): yield from tokbuf.spool() tokbuf.append(t) elif t[1] == ")": nt1 = next(token_stream) nt2 = next(token_stream) if nt1[1] == "=" and nt2[1] == ">": yield (tokenize.NAME, "lambda") yield from tokbuf.tokens[1:] tokbuf.clear() yield (tokenize.OP, ":") else: yield from tokbuf.tokens tokbuf.clear() yield t yield nt1 yield nt2 elif not tokbuf.empty(): tokbuf.append(t) else: yield t def hook(modname, filename): with open(filename, "rb") as f: # Fairly speaking, tokenizing just to convert back to string form # isn't too efficient, but CPython doesn't offer us a way to parse # token stream so far, so we have no choice. source = tokenize.untokenize(xform(tokenize.tokenize(f.readline))) mod = type(imphook)(modname) exec(source, vars(mod)) return mod imphook.add_import_hook(hook, (".py",)) =========== -- Best regards, Paul mailto:pmiscml@gmail.com [View Less]

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PEP 9999 (provisional): support for indexing with keyword arguments
by Stefano Borini March 10, 2021

March 10, 2021

PEP for support for indexing with keyword arguments is now submitted as PR. https://github.com/python/peps/pull/1612 Thanks to everybody involved in the development of the PEP and the interesting discussion. All your contributions have been received and often added to the document. If the PEP is approved, I would like to attempt an implementation, but I am not particularly skilled in the python internals. If a core developer is willing to teach me the ropes (especially in the new parser, I … [View More]

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A shortcut to load a JSON file into a dict : json.loadf
by The Nomadic Coder March 10, 2021

March 10, 2021

Hi All, This is the first time I'm posting to this mailing group, so forgive me if I'm making any mistakes. So one of the most common ways to load json, is via a file. This is used extensively in data science and the lines. We often write something like :- with open(filename.json, "r") as f: my_dict = json.load(f) or my_dict = json.load(open("filename.json", "r")) Since this is sooooo common, why doesn't python have something like :- json.loadf("filename.json") Is there an obvious … [View More]

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SimpleNamespace vs object
by Sven R. Kunze March 2, 2021

March 2, 2021

Starting this as a new thread for the interested reader: On 17.02.21 11:18, Chris Angelico wrote: > On Wed, Feb 17, 2021 at 9:11 PM Sven R. Kunze <srkunze(a)mail.de> wrote: >> Still think that "object()" should be writable since this seems like an >> arbitrary restriction (+SimpleNamespace is no builtin and at least I >> would use object() for fast PoCs or dirty hackery). But I guess there's >> been discussion around this already. >> [...] > Using … [View More]

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Have virtual environments led to neglect of the actual environment?
by Random832 March 1, 2021

March 1, 2021

I was reading a discussion thread <https://gist.github.com/tiran/2dec9e03c6f901814f6d1e8dad09528e> about various issues with the Debian packaged version of Python, and the following statement stood out for me as shocking: Christian Heimes wrote: > Core dev and PyPA has spent a lot of effort in promoting venv because we don't want users to break their operating system with sudo pip install. I don't think sudo pip install should break the operating system. And I think if it does, that … [View More]

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argparse: mutually inclusive arguments
by Paul Korir Feb. 27, 2021

Feb. 27, 2021

Hi All, I've been using the argparse library for a long time and one use case that repeatedly shows us is the need to have two arguments appear together i.e either both appear or none of them appear. I'll refer to these as *mutually inclusive* in contrast to the existing *mutual exclusive* feature present. I might be wrong but there seems to be no way to enforce this. Of course it is possible to have two arguments that are *required* but it's not always the case that they will be needed. A … [View More]

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Deprecate/change the behaviour of ~bool
by Soni L. Feb. 24, 2021

Feb. 24, 2021

Currently ~False is -1 and ~True is -2. Would be nicer if ~bool was the same as not bool. Hopefully nobody actually relies on this but nevertheless, it would be a backwards-incompatible change so the whole deprecation warnings and whatnot would be required. In particular, this is nice for xnor operator: a ^~ b. This currently works on ints, but not on bools, while most other operators, including xor, do successfully work on bools.

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Re: [Python-Dev] Re: Have virtual environments led to neglect of the actual environment?
by Random832 Feb. 24, 2021

Feb. 24, 2021

I accidentally removed Python-Ideas from the recipient list while posting this reply. On Wed, Feb 24, 2021, at 09:16, Random832 wrote: > On Wed, Feb 24, 2021, at 06:27, Christian Heimes wrote: > > Separate directories don't prevent clashes and system breakage. But they > > provide an easy way to *recover* from a broken system. > > I think it could be turned into a way to prevent them by A) having > site-packages always take precedence over dist-packages [i believe … [View More]

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Re: [Python-Dev] Re: Have virtual environments led to neglect of the actual environment?
by Henk-Jaap Wagenaar Feb. 24, 2021

Feb. 24, 2021

On Wed, 24 Feb 2021 at 10:18, Antoine Pitrou <antoine(a)python.org> wrote: > On Tue, 23 Feb 2021 20:29:52 -0500 > Jonathan Goble <jcgoble3(a)gmail.com> wrote: > > > > I can't speak for distributors or maintainers [1], but I can speak for > > myself as a user. I run Debian testing (currently bullseye as that is > > preparing for release) as my daily OS on my personal laptop, used for > > personal matters and school assignments (I'm a university … [View More]

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Alternate lambda syntax
by J. Pic Feb. 24, 2021

Feb. 24, 2021

Hi all, Lambdas can be defined as such: w = lambda: [12] x = lambda y: len(y) I'd like to propose the following: w = (): [12] x = (y): len(y) Or even another contraction for when there are no arguments: w =: [12] This would also be consistent with the other proposal on anonymous functions for defaults: https://mail.python.org/pipermail/python-list/2021-February/900795.html -- ∞

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