bpo-30618: add readlink to pathlib.Path

[girtsf]

This adds a "readlink" method to pathlib.Path objects that calls through
to os.readlink.

https://bugs.python.org/issue30618

Automerge-Triggered-By: @gpshead

[the-knights-who-say-ni]

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[girtsf]

I submitted the CLA form, so it will probably take a few days to clear.

Also, I wasn't entirely sure if a) this needs any special handling for non-POSIX platforms, and b) if I'm supposed to be modifying the documentation in this pull request too, so any advice would be welcome!

[ammaraskar]

a) this needs any special handling for non-POSIX platforms

Take a look at is_mount for some prior art on this, it throws a NotImplementedError on Windows and the documentation notes that its not available on Windows.

b) if I'm supposed to be modifying the documentation in this pull request too, so any advice would be welcome!

Documentation should definitely be added since this is a public facing API.

Edit: it looks like windows actually does support os.readlink in Py3 so it should be made available there.

[girtsf]

Updated the pull request to include documentation. Also, switched to wrapping the readlink value in Path, to have similar behavior to existing functions (e.g., 'resolve').

(Also, I submitted the CLA couple weeks ago, not sure if somebody needs to kick the CLA bot or if it will automagically happen?)

[girtsf]

Hmm. So looks like this is failing on windows with:

======================================================================
ERROR: test_readlink (test.test_pathlib.PathTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\a\1\s\lib\test\test_pathlib.py", line 1671, in test_readlink
    self.assertEqual((P / 'linkA').readlink(), self.cls('fileA'))
  File "D:\a\1\s\lib\pathlib.py", line 1204, in readlink
    path = self._accessor.readlink(self)
  File "D:\a\1\s\lib\pathlib.py", line 424, in readlink
    return os.readlink(path)
TypeError: readlink() argument 1 must be str, not WindowsPath

Is this a bug? The documentation for os.readlink says that it accepts a path-like object. os.readlink(pathlib.Path('foo')) works for me on macOS. Looks like it does not work on windows?

[girtsf]

(Something was wacky with my bpo user, perhaps because I registered with google's oauth. I changed my username, it then cleared out my github username. I reset that back, and now https://bugs.python.org/user?@template=clacheck&github_names=girtsf shows true. Dear Ni bot tamers, can we try again with that label please?)

[girtsf]

FYI: filed https://bugs.python.org/issue34384 for the readlink on Windows issue.

[girtsf]

Hooray, looks like due to @berkerpeksag 's fixes in #8740, the tests now pass on Windows too!

I think this is ready for another looksie.

[berkerpeksag]

@girtsf thanks for the ping! I just added this to my TODO list.

[berkerpeksag]

Please add a note to Doc/whatsnew/3.8.rst and use the following format:

Your note.

(Contributed by Girts Folkmanis in :issue:`30618`.)

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[csabella]

@girtsf, please address the code review from @berkerpeksag. Thanks!

[girtsf]

Better later than never? 😬

I'm assuming 3.8 train has sailed, so I added the news to 3.9.

I have made the requested changes; please review again.

[bedevere-bot]

Thanks for making the requested changes!

@berkerpeksag: please review the changes made to this pull request.

[girtsf]

@gpshead, um, hi! Abusing old connections to see if I can get this reviewed. :)

[gpshead]

the azure pipelines should've completed within half an hour after yesterday's push but appear to have not even run it? odd. i'm closing and reopening to kick the CI systems to rerun.

[miss-islington]

@girtsf: Status check is done, and it's a success ✅ .