re match.group should support __index__

[jdemeyer]

BPO	27177
Nosy	@ezio-melotti, @serhiy-storchaka, @jdemeyer, @zhangyangyu
Files	re_match_index.patch: Patch for Python 2.7 issue27177.patch

^{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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-06-18.14:13:40.038>
created_at = <Date 2016-06-01.14:20:08.737>
labels = ['expert-regex', 'type-feature']
title = 're match.group should support __index__'
updated_at = <Date 2016-06-18.14:13:40.037>
user = 'https://github.com/jdemeyer'

bugs.python.org fields:

activity = <Date 2016-06-18.14:13:40.037>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-06-18.14:13:40.038>
closer = 'serhiy.storchaka'
components = ['Regular Expressions']
creation = <Date 2016-06-01.14:20:08.737>
creator = 'jdemeyer'
dependencies = []
files = ['43084', '43396']
hgrepos = []
issue_num = 27177
keywords = ['patch']
message_count = 9.0
messages = ['266817', '266822', '266884', '266885', '268606', '268775', '268797', '268800', '268804']
nosy_count = 6.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'python-dev', 'serhiy.storchaka', 'jdemeyer', 'xiang.zhang']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27177'
versions = ['Python 3.6']

[jdemeyer]

>>> class zero(object):
...     def __index__(self):
...         return 0
... 
>>> z = zero()
>>> import re
>>> p = re.compile('(a)b')
>>> m = p.match('ab')
>>> m.group(0)
'ab'
>>> m.group(z)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: no such group

[serhiy-storchaka]

This looks as new feature and can go only in 3.6.

[jdemeyer]

I would still argue that it's a bug. The intention of PEP-357 is that __index__ should be used whenever some object needs to be converted to a Py_ssize_t, which is exactly what you do here.

[mrabarnett]

It would be a bug if it was supported but gave the wrong result.

It has never been supported (the re module predates PEP-357), so it's a new feature.

[zhangyangyu]

Attach a patch to add this feature to Py3.6.

[serhiy-storchaka]

What is the use case?

[jdemeyer]

My use case is SageMath: http://trac.sagemath.org/ticket/20750

[serhiy-storchaka]

Interesting. This is very unusual but reasonable use case.

[python-dev]

New changeset 0303ab246152 by Serhiy Storchaka in branch 'default':
Issue bpo-27177: Match objects in the re module now support index-like objects
https://hg.python.org/cpython/rev/0303ab246152