The range() object is deepcopied as atomic

[serhiy-storchaka]

BPO	26202
Nosy	@freddrake, @vstinner, @avassalotti, @ethanfurman, @serhiy-storchaka
Files	deepcopy_range.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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-01-28.19:46:46.805>
created_at = <Date 2016-01-25.20:53:06.176>
labels = ['type-bug', 'library']
title = 'The range() object is deepcopied as atomic'
updated_at = <Date 2020-05-28.08:15:50.321>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-05-28.08:15:50.321>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-01-28.19:46:46.805>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2016-01-25.20:53:06.176>
creator = 'serhiy.storchaka'
dependencies = []
files = ['41714']
hgrepos = []
issue_num = 26202
keywords = ['patch']
message_count = 10.0
messages = ['258921', '258925', '258926', '258927', '258929', '258930', '259154', '259155', '370167', '370174']
nosy_count = 6.0
nosy_names = ['fdrake', 'vstinner', 'alexandre.vassalotti', 'ethan.furman', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26202'
versions = ['Python 3.5', 'Python 3.6']

[serhiy-storchaka]

The range() object is immutable, but is not atomic, and copy.deepcopy() shouldn't return it unchanged.

>>> class I(int): pass  # mutable index
... 
>>> import copy
>>> r = range(I(10))
>>> r2 = copy.deepcopy(r)
>>> r.stop.attr = 'spam'
>>> r2.stop.attr
'spam'

This is Python 3 only issue because in 2.7 the xrange() object doesn't exposes start/stop/step attributes.

Proposed patch fixes the copy module.

[vstinner]

Hum ok, it's a bug :-) It should be fixed. Do you want to work on a patch?

[ethanfurman]

I don't have much experience with the copy module, but I don't see any problems with the code.

Does copy.copy suffer from the same problem? If yes, is it fixed with this same patch, or is more work needed?

[ethanfurman]

Victor, patch was already attached. ;)

[vstinner]

deepcopy_range.patch looks good to me.

[serhiy-storchaka]

Returning the same range() object from copy.copy() is correct. This is shallow copying.

[python-dev]

New changeset 5772eae17a82 by Serhiy Storchaka in branch '3.5':
Issue bpo-26202: copy.deepcopy() now correctly copies range() objects with
https://hg.python.org/cpython/rev/5772eae17a82

New changeset d5d0b62c2830 by Serhiy Storchaka in branch 'default':
Issue bpo-26202: copy.deepcopy() now correctly copies range() objects with
https://hg.python.org/cpython/rev/d5d0b62c2830

[serhiy-storchaka]

Thanks Victor.

[serhiy-storchaka]

New changeset 5f4b229 by Serhiy Storchaka in branch 'master':
bpo-40792: Make the result of PyNumber_Index() always having exact type int. (GH-20443)
5f4b229

[serhiy-storchaka]

This change has been reverted in bpo-40792. The range object attributes has now exact type int, so the original issue with deep copying is gone.