Inconsistent behaviour in os.path.islink for symbolic links to directories

[igordertigor]

Bug report

Bug description:

I am finding inconsistent behavior for os.path.islink for symbolic links to directories. Here is a minimal example:

Setup (bash on Ubuntu focal):

mkdir directory
touch directory/file
ln -s directory directory_link
ln -s directory/file file_link

I would expect os.path.link to return False for directory and directory/file but to return True for directory_link and file_link. However, os.path.link("directory_link") == False (the others are as expected).

It might be that the term "existing directory entry" in the documentation means that os.path.link would always be False for links to directories, however that would be inconsistent with the documentation os.path.isdir, which says "both islink() and isdir() can be true for the same path".

The described behaviour for os.path.link differs from the behaviour of pathlib: pathlib.Path("directory_link").is_symlink() == True.

I can see two possible solutions here:

1. os.path.link("directory_link") returns True. This appears to be consistent with both pathlib and the bash-expression [[ -L "directory_link" ]] and I feel that it's preferable.
2. The documentation should be less ambiguous and maybe state clearly that os.path.link is only ever true for files. In addition, this would probably also mean adjusting the documentation for os.path.isdir.

I'm happy to help with either.

CPython versions tested on:

3.11

Operating systems tested on:

Linux

[jwilk]

I can't reproduce it here:

$ mkdir directory
$ touch directory/file
$ ln -s directory directory_link
$ ln -s directory/file file_link
$ python3.11
Python 3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> os.path.islink("directory_link")
True

[igordertigor]

This is getting even more confusing. If I run python interactively as @jwilk reports, I can't reproduce it either. However, when writing a file with the following content:

import os.path

print(f'Directory: {os.path.islink("directory/") = }')
print(f'Directory link: {os.path.islink("directory_link/") = }')
print(f'File: {os.path.islink("directory/file") = }')
print(f'File link: {os.path.islink("file_link") = }')

and running that file with python3.11 test_os.py, I get:

Directory: os.path.islink("directory/") = False
Directory link: os.path.islink("directory_link/") = False
File: os.path.islink("directory/file") = False
File link: os.path.islink("file_link") = True

This is python 3.11.4, but again, I get the exact same behaviour as @jwilk but only in an interactive session, not in a script.

[jwilk]

I think this is the difference you're seeing:

>>> os.path.islink("directory_link")
True
>>> os.path.islink("directory_link/")
False

This is as expected, because directory_link/ is not a symlink; it's a real directory that happens to have a symlink as one of the path components.
You get the same results with the stat command:

$ stat directory_link | head -n2
  File: directory_link -> directory
  Size: 9         	Blocks: 0          IO Block: 4096   symbolic link
$ stat directory_link/ | head -n2
  File: directory_link/
  Size: 4096      	Blocks: 8          IO Block: 4096   directory

[jwilk]

Now, there's also:

>>> pathlib.Path('directory_link').is_symlink()
True
>>> pathlib.Path('directory_link/').is_symlink()
True

but that's a bug in pathlib: #65238

[igordertigor]

Thank you @jwilk , that make sense.