Mailman 3 February 2022 - Python-ideas

Missing expandvars equivalent in pathlib
by anthony.flury Feb. 14, 2022

Feb. 14, 2022

All, I know that /os.path/ includes a function /expandvars(..)/ which expands any environment variables in a given path, but from looking at the /pathlib/ documentation It seems there is no equivalent to /os.path.expandvars(..) on any class/ in /pathlib/, and the recommendation seems to be to use /pathlib/ to do any and all path manipulations, with the exception of expanding environment variables. It appears that the recommended /pathlib/ compatible code to fully convert any file path (which may have environment variables and or ~ or ~user constructs) to a fully resolved absolute path is : import os.path import pathlib given_path = input('Provide the full path') abs_path = pathlib.Path(os.path.expandvars(pathlib.Path(givenpath).expanduser())).resolve() It seems to me that /pathlib.Path/ would benefit massively from an /os.path.expandvars(..)/ equivalent - so that the equivalent code could be : import os.path import pathlib given_path = input('Provide the full path') abs_path = pathlib.Path(givenpath).expandvars().expanduser().resolve() I know the need to do this is likely to be a corner case, but even still it continues dependency on /os.path/ for those programs that need to resolve environment variables in paths, and increases the cognitive load for this operation, , and it seems like a missed feature in /pathlib/ A change such as this shouldn't affect backwards compatibility. What do people think - have I missed something or is pathlib missing something ? /Pathlib documentation / /https://docs.python.org/3/library/pathlib.html#module-pathlib/ -- Anthony Flury *Moble*: +44 07743 282707 *Home*: +44 (0)1206 391294 *email*: anthony.flury(a)btinternet.com

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Re: Please consider mentioning property without setter when an attribute can't be set
by Bruce Leban Feb. 13, 2022

Feb. 13, 2022

I think the more useful message would be something along the lines of AttributeError: can't set attribute 'f' on object of type 'D' This will help you track down the error. Steven D'Aprano listed three reasons why it might fail which sounds right but frequently the underlying reason is something else: You're trying to set the attribute on the wrong object (e.g., element.color vs. element.style.color). I wish more error messages identified the types of the objects involved. --- Bruce > >

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Mapping unpacking assignment
by Yurii Karabas Feb. 12, 2022

Feb. 12, 2022

I am proposing to add smth like JS destructing assignment to python. Basically, it will allow unpacking any mapping (should have __getitem__ and keys() methods) into variables. Proposed syntax: ``` m = {"a": 1, "b": 2, "c": 3, "d": 4} {a, b} = m # a: 1, b: 2 {a, b, **rest} = m # a: 1, b: 2, rest: {c: 3, d: 4} ``` It will be rawly equal to: ``` m = {"a": 1, "b": 2, "c": 3, "d": 4} # {a, b} = m a = m["a"] b = m["b"] # {a, b, **rest} rest = {**m} a = rest.pop("a") b = rest.pop("b") ``` This is fully backward compatible feature because currently syntax like above is not supported: ``` {a, b} = m # a: 1, b: 2 ^^^^^^ SyntaxError: cannot assign to set display here. Maybe you meant '==' instead of '='? ```

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Datetime operation in itertools count
by Aman Pandey Feb. 11, 2022

Feb. 11, 2022

I wanted to generate all the dates between two date ranges for which I was using count function in the itertools and to my surprise count function doesn't support datetime operation. For example >import datetime >from itertools import count >count(datetime.date.today(), datetime.timedelta(1)) Why is count function only limited to numbers shouldn't we make it generic that it should support operation like datetime where addition between the objects is possible. Would like to hear thoughts from you people.

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urllib: addressing inflexibility in scheme-based joining
by Lincoln Auster Feb. 11, 2022

Feb. 11, 2022

Hi, About a month ago, I opened BPO 46337 with regard to urllib's inflexible handling of URL schemes. (Another discussion (from 2013) occured in BPO-18828.) In my ticket, I proposed supplementing the hard-coded uses_* scheme lists that control URL parsing and joining behavior with an enum that may override behavior when calling a function that would effect it. (More detail is available in BPO 46337 and potential code is available in cpython PR#30520.) Do you think this would be a generally useful/good thing to have? Comments, questions, feedback? This would be my first interaction with Python development, so I'm not too certain about where everything goes. Rereading the dev docs, it looks like the appropriate channel for discussion of this is on this mailing list, not BPO. Github just reminded me that my PR is stale, so I figured I'd retry this whole thing with a closer look at the dev documentation - thanks for bearing with me :) -- Lincoln Auster They/Them

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Generics alternative syntax
by Abdulla Al Kathiri Feb. 9, 2022

Feb. 9, 2022

Hello all, Sorry to bother you again with the generic thing. Golang will soon release a new version with Generics. I like their way of doing it. Like Rust, they don’t bother with TypeVars. It makes you wonder why we are not doing something similar in Python. [T: Type] ——> T is invariant and Type is the bound. [T] is Ok. [T_co:: Type] ——> T is covariant and Type is the bound. [T_co::] is Ok. [T_contra::: Type] —-> T is contravariant and Type is the bound . [T_contra:::] is Ok. Or some other symbol next to : to distinguish the variance. [T: Type1 | Type2] —-> T is invariant and Type1 and Type2 are the constraints. Or anything else to communicate these are constraints (maybe enclose them in parentheses — tuple) Example: class Indexable[T_co::](Protocol[T_co]): def __getitem__(self, n: int) -> T_co: … @dataclass class AInt: seq: list[int] def __getitem__(self, n: int) -> Int: return self.seq[n] @dataclass class BStr: seq: list[str] def __getitem__(self, n: int) -> str: return self.seq[n] def get[T: int | str](n: int, object: Indexable[T]) -> T: return object[n] get(1, AInt([1, 2])) # ok get(1, BStr([“one”, “two”])) # ok Abdulla Sent from my iPhone

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New Web Interface Library For Python?
by Abdur-Rahmaan Janhangeer Feb. 9, 2022

Feb. 9, 2022

Greetings list, Here is a nobody proposing something to be picked up by more skilled people. The urllib deprecation thread is scary for many reasons. I cannot just ignore it as it affects me as a noob user. The security issues makes one think if we continue shipping something that always has known open holes, can we sleep soundly? On the other hand, removing the library completely is weird. How can programming be fun if it does not provide 'internet'-related libraries? Heu, should users start diving into C stuffs? Mere patches will work but seeing advances in 3rd party libraries, one think that to have something comparable in the stdlib seems a big task. A minimal library will work but is it the solution? I had the opportunity to get some ideas about how the asyncio implementation went. Folks who had really amazing async experience helped, even wrote PEPs. I think setting up a workgroup with experienced urllib devs and 3rd party library authors will be very productive. It might be true that the days of batteries included are over, but, it might be more true that space is cheap, the world moves fast and more effort is required than it ever was. The way forward will be deprecating urllib in the real sense of the world until it's peacefully asleep, all while introducing a new library. If we go the minimal version route, it might be a good idea to introduce umbrella libraries. Libraries maintained by core devs, but not included in the stdlib. This allows the stdlib to be leaner, more straight to the point. On installation python can have a command to install those extra libs. Proposing this on -ideas as i no longer understand what the original thread is about. And as stated often, i avoid this module of the stdlib because of its non elegent API. If something's no longer used by normal users, it is maybe the time to do something complete and elegent about it. -- A noob Python user who wants his favourite language to be as good as possible Q: Why not post on the original thread? A: Two core ideas in here: viz proposal to set up a workgroup and the umbrella libraries. As such it feels more natural to post on -ideas than -dev

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ConfigParser: typed ExtendedInterpolation
by Paul Korir Feb. 8, 2022

Feb. 8, 2022

Consider the following config file: [section] some_var = 1 [other_section] other_var = ${section:some_var} My idea would be to have an optional additional argument to perform some implied arithmetic e.g. [other_section] other_var = ${section:some_var:int} + 1 Thoughts? Paul

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Consider moving abstract method checking logic from ABCMeta into object
by Neil Girdhar Feb. 8, 2022

Feb. 8, 2022

Currently, some type checkers rightly complain that a method is decorated with abc.abstractmethod when the class's type does not inherit from ABCMeta. Adding a metaclass is a fairly heavy dependency since you're forced to poison all of your other metaclasses with the same base metaclass. It also brings in possibly unwanted type registration that ABC comes with. Now that abstractmethod's usage is extremely well-understood, would it make sense to move the checking logic out of ABCMeta? It could either be put into object so that no base class is necessary (at the cost of slightly slower class creation), or else in a non-meta base class (say, HasAbstractMethods) now that __init_subclass__ is in all extant versions of Python. Inheriting from such a non-meta base class would avoid the poisoning problem described above. As far as I can tell, neither solution breaks code. Best, Neil

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Literal type alternative syntax
by Abdulla Al Kathiri Feb. 5, 2022

Feb. 5, 2022

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