inspect.getdoc could examine the __class__ cell for dynamically generated subclasses

[anntzer]

BPO	38603
Nosy	@1st1, @anntzer
PRs	bpo-38603: Inherit docstrings in dynamically generated subclasses if possible #16957

^{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 2019-10-27.15:24:34.311>
labels = ['library', '3.9']
title = 'inspect.getdoc could examine the __class__ cell for dynamically generated subclasses'
updated_at = <Date 2019-11-24.20:44:00.320>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2019-11-24.20:44:00.320>
actor = 'BTaskaya'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-10-27.15:24:34.311>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 38603
keywords = ['patch']
message_count = 1.0
messages = ['355472']
nosy_count = 2.0
nosy_names = ['yselivanov', 'Antony.Lee']
pr_nums = ['16957']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue38603'
versions = ['Python 3.9']

[anntzer]

Currently, inspect.getdoc() fails to inherit docstrings in dynamically generated subclasses, such as

class Base:
    def method(self): "some docstring"

def make_subclass():
    class subclass(Base):
        def method(self): return super().method()
    return subclass

subclass = make_subclass()
inspect.getdoc(subclass.method)  # => returns None

because inspect._findclass() tries to find the base class by parsing subclass.method.__qualname__ which is "make_subclass.<locals>.subclass.method" and chokes over .<locals>..

In the case where the method does rely on super(), there is another way we can go back to the "owning" class of the method: by looking up the contents of the __class__ cell (which is set up to make 0-arg super()).

Perhaps a __class__ cell could even be set up for all methods defined in dynamically created subclasses (i.e. whose __qualname__ includes .<locals>.), to help with introspection?