python
Objects referencing private-mangled names do not roundtrip properly under pickling.
| BPO | 33007 |
|---|---|
| Nosy | @avassalotti, @serhiy-storchaka, @anntzer, @MojoVampire, @ZackerySpytz |
| PRs |
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']
Linked PRs
- gh-99669
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.
@joeyagreco We have a PR if the author fixes, I can merge after some verification.
Technically, #21480 LGTM. But there is a question -- should we support pickling private methods? They are private for reason -- to prevent the use outside of the class methods. Does pickling and copying fall under this use? For now, when it doesn't work, but you only find out when you try to unpickle it, we're free to solve it one way or another. Either make it officially unsupported and raise an exception when trying to pickle it, or make it working seamlessly like other methods. Note that mangling is an implementation detail of CPython, so there is no guarantee that pickles will be compatible with other Python implementations.
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.