os.path.normpath("//") returns //

[FredRolland]

BPO	26329
Nosy	@malemburg, @ambv, @serhiy-storchaka, @JackMc, @Vgr255, @ArnoCan, @miss-islington, @nanjekyejoannah, @furkanonder
PRs	bpo-26329: update os.path.normpath documentation #20138 [3.10] bpo-26329: update os.path.normpath documentation (GH-20138) #27094 [3.9] bpo-26329: update os.path.normpath documentation (GH-20138) #27095
Files	add-many-slash-path-note.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 2021-07-12.15:23:31.550>
created_at = <Date 2016-02-10.14:58:05.427>
labels = ['3.11', 'type-bug', '3.9', '3.10', 'docs']
title = 'os.path.normpath("//") returns //'
updated_at = <Date 2021-07-12.15:23:31.550>
user = 'https://bugs.python.org/FredRolland'

bugs.python.org fields:

activity = <Date 2021-07-12.15:23:31.550>
actor = 'lukasz.langa'
assignee = 'none'
closed = True
closed_date = <Date 2021-07-12.15:23:31.550>
closer = 'lukasz.langa'
components = ['Documentation']
creation = <Date 2016-02-10.14:58:05.427>
creator = 'Fred Rolland'
dependencies = []
files = ['43250']
hgrepos = []
issue_num = 26329
keywords = ['patch']
message_count = 13.0
messages = ['260016', '260024', '265837', '267400', '267411', '267471', '267478', '267481', '343661', '369084', '397304', '397321', '397328']
nosy_count = 11.0
nosy_names = ['lemburg', 'lukasz.langa', 'serhiy.storchaka', 'Jack.McCracken', 'abarry', 'Winterflower', 'Fred Rolland', 'acue', 'miss-islington', 'nanjekyejoannah', 'furkanonder']
pr_nums = ['20138', '27094', '27095']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26329'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[FredRolland]

Hi,

os.path.normpath("//") returns '//'

I would expect to be '/'

>>> os.path.normpath("//")
'//'
>>> os.path.normpath("///")
'/'
>>> os.path.normpath("////")
'/'

[serhiy-storchaka]

This is a duplicate of bpo-636648.

This is intended behavior. It was introduced in changeset 01d5b80a3c03.

From the POSIX Specification [1]:

"""
A pathname consisting of a single <slash> shall resolve to the root directory of the process. A null pathname shall not be successfully resolved. If a pathname begins with two successive <slash> characters, the first component following the leading <slash> characters may be interpreted in an implementation-defined manner, although more than two leading <slash> characters shall be treated as a single <slash> character.
"""

See also Stack Overflow and Stack Exchange questions: [2], [3], [4].

May be we should add an explanation and a link to the specification in the documentation and comments.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_12
[2] http://stackoverflow.com/questions/7816818/why-doesnt-os-normapath-collapse-a-leading-double-slash
[3] http://unix.stackexchange.com/questions/12283/unix-difference-between-path-starting-with-and
[4] http://unix.stackexchange.com/questions/1910/how-does-linux-handle-multiple-consecutive-path-separators-home-username

[Winterflower]

Should the comment with the link to specification be added to Lib/posixpath.py? or Lib/os.py?

[ArnoCan]

I propose to add at least a statement like e.g. "In conformance to IEEE Std 1003.1™, 2013 Edition; 4.12 Pathname Resolution".

Because I had the same thought of a bug at first view, this because I did not find any hint in e.g. docs for 2.7.11.

The reason to handle this thoroughly in my projects is the application of a path-matching library for generic unit tests, e.g. for bash scripts which require intensive PATH resolution. This has to be applied by the users of the library.

See "https://pypi.python.org/pypi/pyfilesysobjects", and "https://pypi.python.org/pypi/epyunit" which requires intensive pattern matching of application provided pathnames, e.g. when it comes to automatic split of actual used PYTHONPATH items for a specific function/method, module, or package.

E.g. the user provides an 'intentional casual' pathname for drop-in unit tests(see epyunit),
"os.sep + context.sys.path[x] + os.sep + 'rel-module-path'",
due to mixed relative and absolute paths resulting in leading
"os.sep + os.sep".
The pattern match than fails, but it is not immediately clear for which reason.

[serhiy-storchaka]

Could you provide a patch Arno-Can?

According to the comment in the configure script of GNU coreutils, the only POSIX platforms known for coreutils developers that have two distinct roots / and // are Cygwin, z/OS and dead Apollo DomainOS. Yet few exotic platforms are mentioned in the topic at http://comments.gmane.org/gmane.comp.standards.posix.austin.general/11947 .

[ArnoCan]

Hi Serhiy,
I am currently still investigating it for my own project.

https://stackoverflow.com/questions/37646103/posix-path-1003-1-examples-and-behaviour-for-foo-bar

Currently I do not have the build environment, so I can provide the text, but because I am a bit under pressure with finishing a larger pack of OpenSource projects currently I cannot manage to setup the environment.

So can do this eventually in 2-3Weeks.

[JackMc]

Hey all - I would love to write a patch :) Working on it!

[JackMc]

Here's the patch I made.

[nanjekyejoannah]

@ Jack McCracken do you want to open a pull request for this?