The results from os.path.isdir(...) an Path(...).is_dir() are not equivalent for empty path strings.

[godaygo]

BPO	37688
Nosy	@brettcannon, @pitrou, @serhiy-storchaka, @godaygo

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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assignee = None
closed_at = None
created_at = <Date 2019-07-26.07:23:57.873>
labels = ['type-feature', 'library', 'docs']
title = 'The results from os.path.isdir(...) an Path(...).is_dir() are not equivalent for empty path strings.'
updated_at = <Date 2019-07-29.18:50:44.722>
user = 'https://github.com/godaygo'

bugs.python.org fields:

activity = <Date 2019-07-29.18:50:44.722>
actor = 'brett.cannon'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Library (Lib)']
creation = <Date 2019-07-26.07:23:57.873>
creator = 'godaygo'
dependencies = []
files = []
hgrepos = []
issue_num = 37688
keywords = []
message_count = 8.0
messages = ['348475', '348477', '348478', '348482', '348495', '348497', '348528', '348679']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'pitrou', 'docs@python', 'serhiy.storchaka', 'godaygo']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue37688'
versions = []

[godaygo]

In the documentation it is said that os.path.isdir(...) an Path(...).is_dir()are equivalent substitutes.
https://docs.python.org/3/library/pathlib.html#correspondence-to-tools-in-the-os-module

But they give different result for empty path strings:
>>> import os
>>> from pathlib import Path
>>> dummy = "" 
>>> os.path.isdir(dummy)
 False

Obviously it's not an equivalence, so either this should be noted in the documentation or corrected in the code.

[godaygo]

Forgot to write the result for Path variant:

>>> Path(dummy).is_dir()
 True

[serhiy-storchaka]

It is because Path() == Path('') == Path('.').

[godaygo]

I understand the reasons, I only say that it does not correspond to my perception of their equivalence, because:

os.path.isdir('') != os.path.isdir('.')

while:

Path('').is_dir() == Path('.').is_dir()

and I can confirm that some libraries rely on os.path.isdir('') -> False behavior.

[brettcannon]

I think you're reading "equivalence" too strictly here to mean "exactly the same semantics". In this instance it means "for similar functionality, the equivalent method is ..." (admittedly this might be a quirk of the use of the word "equivalent" in North American English).

But I can see why you would interpret it the way you do. Please feel free to propose a PR to clarify the phrasing.

[pitrou]

If "equivalent" is deceiving, perhaps replace it with "similary" or "roughly equivalent". Feel free to post a PR with your preferred wording.

[godaygo]

I am reading "equivalence" too strictly (like "as a substitute"), because this is part of the documentation :) and I agree that in ordinary speech I would use it rather in the sense of “similar”.

In order to make sure, that everyone agrees only on that this requires only a documentation change? Because as for me, I think that it will better for os.path.isdir to raise ValueError or DeprecationWarning - False on empty string is not well defined behavior. But I'm fine to be alone with the last one.

[brettcannon]

Changing the semantics of os.path.isdir() for something like this isn't worth breaking code; basically it's now a quirk of the function.