pathlib strips trailing slash

@akuchling

BPO	21039
Nosy	@akuchling, @pitrou, @serhiy-storchaka, @sigmavirus24, @hvenev
Files	pathlib.patch: patch

^{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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GitHub fields:

assignee = None
closed_at = <Date 2015-04-14.16:54:25.933>
created_at = <Date 2014-03-23.13:55:56.401>
labels = ['type-bug', 'library']
title = 'pathlib strips trailing slash'
updated_at = <Date 2015-04-14.16:54:25.932>
user = 'https://github.com/hvenev'

bugs.python.org fields:

activity = <Date 2015-04-14.16:54:25.932>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2015-04-14.16:54:25.933>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2014-03-23.13:55:56.401>
creator = 'h.venev'
dependencies = []
files = ['34586']
hgrepos = []
issue_num = 21039
keywords = ['patch']
message_count = 15.0
messages = ['214581', '214594', '214595', '214596', '214597', '214598', '214599', '214600', '214601', '214604', '224889', '224942', '240930', '240947', '240948']
nosy_count = 7.0
nosy_names = ['akuchling', 'pitrou', 'BreamoreBoy', 'serhiy.storchaka', 'icordasc', 'h.venev', 'ischwabacher']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21039'
versions = ['Python 3.4', 'Python 3.5']

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Some programs' behavior is different depending on whether the path has a trailing slash or not. Examples include ls, cp, mv, ln, rm and rsync. URL paths may also behave differently. For example http://xkcd.com/1 redirects to http://xkcd.com/1/

Boost.Filesystem's path class also supports trailing slashes in paths. C++'s filesystem library proposal is also based on Boost.Filesystem.

Yes, this is by design. The occasional difference between slash-ended and non-slash-ended paths is unexpected and potentially confusing. Moreover, it's not a property of the OS itself - it's just some syntactic sugar to enable an option such as resolving symlinks. pathlib paths represent filesystem paths, not arbitrary shell arguments.

Similarly, pathlib doesn't have special processing for "~someuser" parts.

(as for URL paths, they are not part of the design space of pathlib)

Closing as rejected, sorry.

What about OpenVMS?

Can you elaborate? Python hasn't supported VMS for quite some time...

AFAIK paths on OpenVMS are represented in a strange way. [dir.subdir]filename is a path for a file and [dir.subdir.anothersubdir] is a path for a directory.

Then I'm afraid the current Path classes won't do a good job of representing them :-)

But as I said, Python probably doesn't run on VMS anymore, so this is a rather theoretical problem. Maybe if some day Python supports VMS again, someone can contribute a VMSPath implementation.

Or maybe URLPath?

Or maybe URLPath?

I'm skeptical about that. I think someone should first prototype a
PureURLPath and maybe publish it on PyPI.
(as for the non-pure variant, URLPath, it doesn't seem to make sense)

PEP-11 states that VMS was unsupported in 3.3. Code was removed from 3.4 via bpo-16136.

This may be only syntactic sugar, but it is POSIX-specified syntactic sugar: according to http://pubs.opengroup.org/onlinepubs/9699919799/. trailing slashes in pathnames are semantically meaningful in pathname resolution. Tilde escapes are not mentioned.

4.12 Pathname Resolution
========================

[...]

A pathname that contains at least one non- <slash> character and that ends with one or more trailing <slash> characters shall not be resolved successfully unless the last pathname component before the trailing <slash> characters names an existing directory or a directory entry that is to be created for a directory immediately after the pathname is resolved. Interfaces using pathname resolution may specify additional constraints[1] when a pathname that does not name an existing directory contains at least one non- <slash> character and contains one or more trailing <slash> characters.

If a symbolic link is encountered during pathname resolution, the behavior shall depend on whether the pathname component is at the end of the pathname and on the function being performed. If all of the following are true, then pathname resolution is complete:

1. This is the last pathname component of the pathname.

2. The pathname has no trailing <slash>.

3. The function is required to act on the symbolic link itself, or certain arguments direct that the function act on the symbolic link itself.

In all other cases, the system shall prefix the remaining pathname, if any, with the contents of the symbolic link. [...]

Isaac, thanks for the reference. I'm reopening the issue for discussion (although I'm still not convinced this would be actually a good thing).
May I ask you to post on the python-dev mailing-list for further feedback?

fix: Remove os-dependent pieces of schema validation (#2357)

fix(backport): Remove os-dependent pieces of schema validation

fix(backport): Remove os-dependent pieces of schema validation (#2361)

So maybe an alternative approach could be not to have the behavior be indicated by some property of the Path instance but by using different attributes. So maybe e.g. Path("foo/").name would return "foo" but Path("foo/").alt_name would return "". This would avoid the scenario I described just above.

Now we just have to decide on names for the attributes that could have this alternate behavior (are there others besides .parent and .name?). And probably the implementation will have to keep track of the trailing slash somehow.

I've been working on a patch along these lines. The idea is to ignore any trailing slash whenever we split a path into (dirname, basename). So:

>>> from pathlib import PurePosixPath
>>> p = PurePosixPath('/home/barney/')
>>> p.parent
PurePosixPath('/home')
>>> list(p.parents)
[PurePosixPath('/home'), PurePosixPath('/')]
>>> p.name
'barney'
>>> p.with_name('fred')
PurePosixPath('/home/fred/')

This also applies to [with_]stem, [with_]suffix, suffixes, [is_]relative_to.

Users wouldn't be able to call path.parent to remove a trailing slash, so we'd need to add something like PurePath.[with_]trailer I think.

pythonGH-65238: Preserve trailing slash in pathlib

pythonGH-106747: Improve `glob()` expectations in pathlib tests

GH-106747: Improve `Path.glob()` expectations in pathlib tests (#112365)

pythonGH-65238: Add test cases for trailing slash handling in pathlib

Re-resolving as "won't fix" - the present behaviour is desirable for many users and it's too dangerous to change now. The crux of the issue is:

>>> str(PurePath('a/')) == 'a'
True
>>> PurePath('a/') == PurePath('a')
True

Fixing this bug entails changing the first result, which entails changing the second too. For some this is clearly a bugfix, but for many others it comes close to defeating the purpose of pathlib.

I don't think an initialiser argument would help: users handed a Path object would still need to cope with the possible equality and string representation change.

Much more discussion here: https://discuss.python.org/t/pathlib-preserve-trailing-slash/33389/

pythonGH-106747: Improve `Path.glob()` expectations in pathlib tests (p…

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pathlib strips trailing slash #65238

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hvenev commented on Mar 23, 2014

pitrou commented on Mar 23, 2014

pitrou commented on Mar 23, 2014

hvenev commented on Mar 23, 2014

pitrou commented on Mar 23, 2014

hvenev commented on Mar 23, 2014

pitrou commented on Mar 23, 2014

hvenev commented on Mar 23, 2014

pitrou commented on Mar 23, 2014

BreamoreBoy commented on Mar 23, 2014

ischwabacher commented on Aug 5, 2014

pitrou commented on Aug 6, 2014

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barneygale commented on Nov 24, 2023

barneygale commented on Dec 19, 2023

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