pathlib.PurePath.with_suffix() does not allow removing the suffix

[tifv]

BPO	20639
Nosy	@pitrou, @tifv, @serhiy-storchaka
Files	pathlib-with_suffix-test.diff: proposed tests pathlib-with_suffix.diff: proposed fix

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2014-07-07.01:39:34.620>
created_at = <Date 2014-02-16.13:28:50.211>
labels = ['type-bug', 'library']
title = 'pathlib.PurePath.with_suffix() does not allow removing the suffix'
updated_at = <Date 2014-07-07.01:39:34.619>
user = 'https://github.com/tifv'

bugs.python.org fields:

activity = <Date 2014-07-07.01:39:34.619>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2014-07-07.01:39:34.620>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2014-02-16.13:28:50.211>
creator = 'july'
dependencies = []
files = ['34099', '34100']
hgrepos = []
issue_num = 20639
keywords = ['patch']
message_count = 5.0
messages = ['211316', '211317', '211766', '222428', '222430']
nosy_count = 4.0
nosy_names = ['pitrou', 'july', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue20639'
versions = ['Python 3.4', 'Python 3.5']

[tifv]

The changeset ef2b2ddd27c8 restricted the argument of Path.with_suffix() too much, and caused some strange behavior.

Case 1: removing suffix completely is disallowed now.
The following code worked before the fix:

>>> pathlib.PurePath('a', 'b.c').with_suffix('')
PurePosixPath('a/b')

but now fails with ValueError:

>>> pathlib.PurePath('a', 'b.c').with_suffix('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/july/source/python/Lib/pathlib.py", line 760, in with_suffix
    raise ValueError("Invalid suffix %r" % (suffix))
ValueError: Invalid suffix ''

It was the only one obvious way of removing the suffix, and I think it should remain so. (BTW: There is a XXX note in the code questioning if Path.with_suffix(None) should remove the suffix.)

Case 2: while the output is now always a correct Path, the suffix can still contain separator.
The following code produced incorrect path before the fix:

>>> pathlib.PurePath('a', 'b.c').with_suffix('./.s/.')
PurePosixPath('a/b./.s/.')
>>> _.parts
('a', 'b./.s/.')

Now, the produced path is correct, but the code itself is still allowed:

>>> pathlib.PurePath('a', 'b.c').with_suffix('./.s/.')
PurePosixPath('a/b.s')

while I would expect it to fail with ValueError.

Attached: proposed test patch.

[tifv]

Proposed patch attached.

[pitrou]

Thank you! Unfortunately, it is too late for 3.4, but I will make sure the fix is included in 3.4.1 (and 3.5).

[python-dev]

New changeset 0d84855861ff by Antoine Pitrou in branch '3.4':
Issue bpo-20639: calling Path.with_suffix('') allows removing the suffix again.
http://hg.python.org/cpython/rev/0d84855861ff

[pitrou]

Sorry for the delay! The patch is now applied. Thank you for contributing!