[issue31107] copyreg does not properly mangle __slots__ names

[Shane Harvey]

New submission from Shane Harvey:

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.

----------
components: Library (Lib)
messages: 299665
nosy: Shane Harvey
priority: normal
severity: normal
status: open
title: copyreg does not properly mangle __slots__ names
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue31107>
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