New submission from QbLearningPython <quib...@hotmail.com>:
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, 16:18:25)
[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.
--
components: Library (Lib)
messages: 317790
nosy: QbLearningPython
priority: normal
severity: normal
status: open
title: pathlib.Path.resolve() returns path with double slash when resolving a
relative path
