copyreg does not properly mangle __slots__ names

[ShaneHarvey]

BPO	31107
Nosy	@serhiy-storchaka, @ShaneHarvey
PRs	bpo-31107: Fix copyreg mangled slot names calculation. #2989 [3.6] bpo-31107: Fix copyreg mangled slot names calculation. (GH-2989) #3003 [2.7] bpo-31107: Fix copyreg mangled slot names calculation. (GH-2989). #3004

^{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 2017-08-05.15:24:03.870>
created_at = <Date 2017-08-02.18:53:14.769>
labels = ['3.7', 'type-bug', 'library']
title = 'copyreg does not properly mangle __slots__ names'
updated_at = <Date 2017-08-05.15:24:03.861>
user = 'https://github.com/ShaneHarvey'

bugs.python.org fields:

activity = <Date 2017-08-05.15:24:03.861>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2017-08-05.15:24:03.870>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2017-08-02.18:53:14.769>
creator = 'ShaneHarvey'
dependencies = []
files = []
hgrepos = []
issue_num = 31107
keywords = []
message_count = 4.0
messages = ['299665', '299737', '299787', '299788']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'ShaneHarvey']
pr_nums = ['2989', '3003', '3004']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31107'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7']

[ShaneHarvey]

This line in copyreg._slotnames does not properly calculate mangled attribute names:
https://github.com/python/cpython/blob/v3.6.2/Lib/copyreg.py#L131

The problem is that it does not strip leading underscores from the class name:

>>> class _LeadingUnderscoreClassName(object):
...     __slots__ = ("__bar",)
...
>>> import copy_reg
>>> copy_reg._slotnames(_LeadingUnderscoreClassName)
['__LeadingUnderscoreClassName__bar']

The result is that copy, pickle, and anything else that relies on _slotnames() do not work on classes with leading underscores and private __slots__. This bug is present in all versions of Python.

[serhiy-storchaka]

New changeset c4c9866 by Serhiy Storchaka (Shane Harvey) in branch 'master':
bpo-31107: Fix copyreg mangled slot names calculation. (bpo-2989)
c4c9866

[serhiy-storchaka]

New changeset 4795ba8 by Serhiy Storchaka (Shane Harvey) in branch '3.6':
[3.6] bpo-31107: Fix copyreg mangled slot names calculation. (GH-2989) (bpo-3003)
4795ba8

[serhiy-storchaka]

New changeset 88ffff5 by Serhiy Storchaka (Shane Harvey) in branch '2.7':
[2.7] bpo-31107: Fix copyreg mangled slot names calculation. (GH-2989). (bpo-3004)
88ffff5