Objects referencing private-mangled names do not roundtrip properly under pickling.

@avassalotti

BPO	33007
Nosy	@avassalotti, @serhiy-storchaka, @anntzer, @MojoVampire, @ZackerySpytz
PRs	gh-77188: Add support for pickling private methods and nested classes #21480

^{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 = None
closed_at = None
created_at = <Date 2018-03-06.05:36:52.125>
labels = ['3.8', 'library', '3.9', '3.10']
title = 'Objects referencing private-mangled names do not roundtrip properly under pickling.'
updated_at = <Date 2020-07-15.17:51:11.385>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2020-07-15.17:51:11.385>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2018-03-06.05:36:52.125>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 33007
keywords = ['patch']
message_count = 2.0
messages = ['313306', '349838']
nosy_count = 5.0
nosy_names = ['alexandre.vassalotti', 'serhiy.storchaka', 'Antony.Lee', 'josh.r', 'ZackerySpytz']
pr_nums = ['21480']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue33007'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

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Consider the following example:

    import pickle

    class T:
        def __init__(self):
            self.attr = self.__foo

        def __foo(self):
            pass

    print(pickle.loads(pickle.dumps(T())))

This fails on 3.6 with AttributeError: 'T' object has no attribute '__foo' (i.e. there's a lookup on the unmangled name). As a comparison, replacing __foo with _foo results in working code.

This problem is specific to private methods AFAICT, since they're the only things which have an unmangled __name__ used to pickle them, but are stored as a mangled name.

More details on cause and solution on issue bpo-37852, which I closed as a duplicate of this issue.

Having this same issue on Python 3.10. Any updates on this?

@joeyagreco

@joeyagreco We have a PR if the author fixes, I can merge after some verification.

@nanjekyejoannah

@nanjekyejoannah I have fixed the PR's merge conflicts.

Since this never worked before, I reclassify this as a new feature.

#21480 only handles private bound methods. Staticmethods, classmethods and unbound methods are not supported.

pythongh-77188: Add pickle tests for objects with slots

gh-77188: Add pickle tests for objects with slots (GH-144116)

pythongh-77188: Add pickle tests for objects with slots (pythonGH-144116

[3.14] gh-77188: Add pickle tests for objects with slots (GH-144116) (G…

[3.13] gh-77188: Add pickle tests for objects with slots (GH-144116) (G…

gh-77188: Add support for pickling private methods and nested classes (…

pythongh-77188: Add pickle tests for objects with slots (pythonGH-144116

pythongh-77188: Add support for pickling private methods and nested c…

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Objects referencing private-mangled names do not roundtrip properly under pickling. #77188

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Objects referencing private-mangled names do not roundtrip properly under pickling. #77188

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anntzer commented on Mar 6, 2018

MojoVampire commented on Aug 16, 2019

joeyagreco commented on Jul 8, 2022

nanjekyejoannah commented on Oct 7, 2022

ZackerySpytz commented on Dec 11, 2022

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serhiy-storchaka commented on Jan 6, 2026

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