[issue29847] Path takes and ignores **kwargs

[Rémi Lapeyre]

Change by Rémi Lapeyre :


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versions: +Python 3.10, Python 3.8, Python 3.9

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[issue29847] Path takes and ignores **kwargs

[Rémi Lapeyre]

Rémi Lapeyre  added the comment:

PurePath subclasses cannot support kwargs as __new__() does not accept **kwargs:


>>> from pathlib import PurePath
>>> class MyPurePath(PurePath):
... def __init__(self, *args, **kargs): pass
... 
>>> MyPurePath('foo', spam=True)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: __new__() got an unexpected keyword argument 'spam'


The behaviour for this should probably be made the same for both Path and 
PurePath.

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[issue29847] Path takes and ignores **kwargs

[Yurii Karabas]

Change by Yurii Karabas <1998uri...@gmail.com>:


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nosy: +uriyyo
nosy_count: 6.0 -> 7.0
pull_requests: +18959
pull_request: https://github.com/python/cpython/pull/19632

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[issue29847] Path takes and ignores **kwargs

[Jason Saporta]

Change by Jason Saporta :


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keywords: +patch
pull_requests: +13309
stage:  -> patch review

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[issue29847] Path takes and ignores **kwargs

[Jakub Stasiak]

Change by Jakub Stasiak :


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nosy: +jstasiak

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[issue29847] Path takes and ignores **kwargs

[Brett Cannon]

Brett Cannon added the comment:

Then I vote for Serhiy's idea of simply raising an exception in the concrete 
subclasses when a keyword argument is given.

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[issue29847] Path takes and ignores **kwargs

[Antoine Pitrou]

Antoine Pitrou added the comment:

> The support of **kwargs in Path.__new__ is needed if you want to implement a 
> subclass of Path with __init__ accepting keyword arguments

I don't remember exactly, but I think this was the intention indeed.  There was 
originally an openat-using subclass, and IIRC it took additional parameters 
(such as the directory fd). That got scrapped quite early in the process, so we 
can remove the **kwargs thing now.

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[issue29847] Path takes and ignores **kwargs

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I don't know whether it was the intension of Antoine or just an oversight. I 
don't know whether it is used in the wild. But we can at least raise a 
TypeError for concrete classes PosixPath and WindowsPath if ignoring keyword 
arguments is a problem. Many extension types don't take keyword arguments, but 
their subclasses accept and ignore keyword arguments. For example:

>>> filter(None, [], foo=123)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: filter() does not take keyword arguments
>>> class X(filter): pass
... 
>>> X(None, [], foo=123)
<__main__.X object at 0xb6fdcacc>

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[issue29847] Path takes and ignores **kwargs

[Brett Cannon]

Brett Cannon added the comment:

Shoot, that's too bad. I guess we should document it then so people are aware 
that keyword arguments are ignored, else we will break subclasses. There's also 
an unfortunate difference between PurePath and Path as PurePath doesn't have 
this quirk.

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[issue29847] Path takes and ignores **kwargs

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The support of **kwargs in Path.__new__ is needed if you want to implement a 
subclass of Path with __init__ accepting keyword arguments (and since Path 
constructor takes variable number of positional arguments, new arguments should 
be keyword-only).

>>> import pathlib
>>> class MyPath(pathlib.PosixPath):
... def __init__(self, *args, spam=False):
... self.spam = spam
... 
>>> p = MyPath('/', spam=True)
>>> p
MyPath('/')
>>> p.spam
True

Removing **kwargs from Path.__new__ will break the above example.

>>> MyPath('/', spam=True)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: __new__() got an unexpected keyword argument 'spam'

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[issue29847] Path takes and ignores **kwargs

[Jelle Zijlstra]

Jelle Zijlstra added the comment:

Thanks, I'll add a PR. This doesn't need to be documented, right?

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[issue29847] Path takes and ignores **kwargs

[Brett Cannon]

Brett Cannon added the comment:

Yep, kwargs should be dropped since it isn't used or documented: 
https://docs.python.org/3/library/pathlib.html#pathlib.PurePath (probably just 
a hold-over from when it did in some earlier version of the code).

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components: +Library (Lib)
nosy: +brett.cannon
type:  -> behavior
versions: +Python 3.7

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[issue29847] Path takes and ignores **kwargs

[Jim Fasarakis-Hilliard]

Changes by Jim Fasarakis-Hilliard :


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[issue29847] Path takes and ignores **kwargs

[Jelle Zijlstra]

New submission from Jelle Zijlstra:

pathlib.Path.__new__ takes **kwargs, but doesn't do anything with them 
(https://github.com/python/cpython/blob/master/Lib/pathlib.py#L979). This 
doesn't appear to be documented.

This feature should presumably be either documented or removed (probably 
removed unless I'm missing some reason for having it).

Brief discussion on a typeshed PR at 
https://github.com/python/typeshed/pull/991#discussion-diff-105813974R100

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nosy: Jelle Zijlstra, pitrou
priority: normal
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status: open
title: Path takes and ignores **kwargs

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