pickle docs are wrong about nested classes

[JelleZijlstra]

BPO	47206
Nosy	@avassalotti, @JelleZijlstra, @maggyero

^{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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assignee = None
closed_at = None
created_at = <Date 2022-04-03.15:10:59.776>
labels = ['3.11', 'type-bug', '3.9', '3.10', 'docs']
title = 'pickle docs are wrong about nested classes'
updated_at = <Date 2022-04-04.16:30:12.057>
user = 'https://github.com/JelleZijlstra'

bugs.python.org fields:

activity = <Date 2022-04-04.16:30:12.057>
actor = 'maggyero'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2022-04-03.15:10:59.776>
creator = 'JelleZijlstra'
dependencies = []
files = []
hgrepos = []
issue_num = 47206
keywords = []
message_count = 1.0
messages = ['416625']
nosy_count = 4.0
nosy_names = ['alexandre.vassalotti', 'docs@python', 'JelleZijlstra', 'maggyero']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47206'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[JelleZijlstra]

https://docs.python.org/3.10/library/pickle.html#what-can-be-pickled-and-unpickled says that only "classes that are defined at the top level of a module" can be pickled. But in fact these work fine in current Python, probably since 3.3 when __qualname__ was added (https://docs.python.org/3/library/stdtypes.html#definition.\_\_qualname__). Similarly, the docs claim only top-level functions can be pickled, but in fact methods nested in classes work fine.

Example script demonstrating that these work:

import pickle


class X:
    class Y:
        pass

    def method(self):
        pass


print(pickle.dumps(X.Y))
print(pickle.loads(pickle.dumps(X.Y)))

print(pickle.dumps(X.Y()))
print(pickle.loads(pickle.dumps(X.Y())))

print(pickle.dumps(X.method))
print(pickle.loads(pickle.dumps(X.method)))