Issue 33660: pathlib.Path.resolve() returns path with double slash when resolving a relative path in root directory (original) (raw)

I have recently found a weird behaviour while trying to resolve a relative path located on the root directory on a macOs.

I tried to resolve a Path('spam') and the interpreter answered PosixPath('//spam') —double slash for root— instead of (my) expected PosixPath('/spam').

I think that this is a bug.

I ran the interpreter from root directory (cd /; python). Once running the interpreter, this is what I did:

import pathlib pathlib.Path.cwd() PosixPath('/')

since the interpreter has been launched from root

p = pathlib.Path('spam') p PosixPath('spam')

just for checking

p.resolve() PosixPath('//spam')

beware of double slash instead of single slash

I also checked the behaviour of Path.resolve() in a non-root directory (in my case launching the interpreter from /Applications).

import pathlib pathlib.Path.cwd() PosixPath('/Applications') p = pathlib.Path('eggs') p PosixPath('eggs') p.resolve() PosixPath('/Applications/eggs')

just one slash as root in this case (as should be)

So it seems that double slashes just appear while resolving relative paths in the root directory.

More examples are:

pathlib.Path('spam/egg').resolve() PosixPath('//spam/egg') pathlib.Path('./spam').resolve() PosixPath('//spam') pathlib.Path('./spam/egg').resolve() PosixPath('//spam/egg')

but

pathlib.Path('').resolve() PosixPath('/') pathlib.Path('.').resolve() PosixPath('/')

Intriguingly,

pathlib.Path('spam').resolve().resolve() PosixPath('/spam')

'spam'.resolve = '//spam'

'//spam'.resolve = '/spam'!!!

pathlib.Path('//spam').resolve() PosixPath('/spam')

I have found the same behaviour in several Python versions:

Python 3.6.5 (default, May 15 2018, 08:20:57) [GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)] on darwin

Python 3.4.8 (default, Mar 29 2018, 16🔞25) [GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin

Python 3.5.5 (default, Mar 29 2018, 16:22:58) [GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin

Python 3.7.0b4 (default, May 4 2018, 22:01:49) [Clang 9.1.0 (clang-902.0.39.1)] on darwin

All running on: macOs High Sierra 10.13.4 (17E202)

There is also confirmation of same issue on Ubuntu 16.04 (Python 3.5.2) and Opensuse tumbleweed (Python 3.6.5)

I have searched for some information on this issue but I did not found anything useful.

Python docs (https://docs.python.org/3/library/pathlib.html) talks about "UNC shares" but this is not the case (in using a macOs HFS+ filesystem).

PEP 428 (https://www.python.org/dev/peps/pep-0428/) says:

Multiple leading slashes are treated differently depending on the path flavour. They are always retained on Windows paths (because of the UNC notation):

>>> PureWindowsPath('//some/path')
PureWindowsPath('//some/path/')

On POSIX, they are collapsed except if there are exactly two leading slashes, which is a special case in the POSIX specification on pathname resolution [8] (this is also necessary for Cygwin compatibility):

>>> PurePosixPath('///some/path')
PurePosixPath('/some/path')
>>> PurePosixPath('//some/path')
PurePosixPath('//some/path')

I do not think that this is related to the aforementioned issue.

However, I also checked the POSIX specification link (http://pubs.opengroup.org/onlinepubs/009...#tag_04_11) and found:

A pathname that begins with two successive slashes may be interpreted in an implementation-defined manner, although more than two leading slashes shall be treated as a single slash.

I do not really think that this can cause a double slashes while resolving a relative path on macOs.

So, I think that this issue could be a real bug in pathlib.Path.resolve() method. Specifically on POSIX flavour.

A user of Python Forum (killerrex) and I have traced the bugs to Lib/pathlib.py:319 in the Python 3.6 repository https://github.com/python/cpython/blob/3...pathlib.py.

Specifically, in line 319:

newpath = path + sep + name

For pathlib.Path('spam').resolve() in the root directory, newpath is '//spam' since:

path is '/'
sep is '/'
name is 'spam'

killerrex has suggested two solutions:

  1. from line 345

    base = '' if path.is_absolute() else os.getcwd() if base == sep: base = '' return _resolve(base, str(path)) or sep

  2. from line 319:

    if path.endswith(sep): newpath = path + name else: newpath = path + sep + name

Thank you.