help(list[int]) fails

[serhiy-storchaka]

BPO	40296
Nosy	@gvanrossum, @serhiy-storchaka, @JelleZijlstra, @miss-islington
PRs	bpo-40296: Fix supporting generic aliases in pydoc #30253 [3.10] bpo-40296: Fix supporting generic aliases in pydoc (GH-30253). #31976 [3.9] [3.10] bpo-40296: Fix supporting generic aliases in pydoc (GH-30253). (GH-31976) #31981
Dependencies	bpo-47042: Fix test_html_doc in test_pydoc

^{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 = <Date 2022-03-19.15:13:37.231>
created_at = <Date 2020-04-15.20:50:17.005>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = 'help(list[int]) fails'
updated_at = <Date 2022-03-19.15:13:37.230>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2022-03-19.15:13:37.230>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2022-03-19.15:13:37.231>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2020-04-15.20:50:17.005>
creator = 'serhiy.storchaka'
dependencies = ['47042']
files = []
hgrepos = []
issue_num = 40296
keywords = ['patch']
message_count = 6.0
messages = ['366558', '366581', '366609', '415473', '415519', '415554']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'serhiy.storchaka', 'JelleZijlstra', 'miss-islington']
pr_nums = ['30253', '31976', '31981']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40296'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[serhiy-storchaka]

>>> help(list[int])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/_sitebuiltins.py", line 103, in __call__
    return pydoc.help(*args, **kwds)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1905, in __call__
    self.help(request)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1964, in help
    else: doc(request, 'Help on %s:', output=self._output)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1684, in doc
    pager(render_doc(thing, title, forceload))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1677, in render_doc
    return title % desc + '\n\n' + renderer.document(object, name)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 381, in document
    if inspect.isclass(object): return self.docclass(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1251, in docclass
    (str(cls.__name__) for cls in type.__subclasses__(object)
TypeError: descriptor '__subclasses__' for 'type' objects doesn't apply to a 'types.GenericAlias' object

[serhiy-storchaka]

The problem is that isinstance(list[int], type) returns True, but list[int] is not actually an instance of type.

>>> isinstance(list[int], type)
True
>>> issubclass(type(list[int]), type)
False
>>> type.__subclasses__(list[int])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: descriptor '__subclasses__' for 'type' objects doesn't apply to a 'types.GenericAlias' object

[gvanrossum]

Yeah, I think help() or pydoc needs to special-case this. (Didn't your other PR attempt to fix this?)

Note that issubclass(list[int].__class__, type) returns True -- the __class__ attribute in this case is taken from __origin__, while type() returns the "true" class.

I don't know what to do about __subclasses__ -- I expect we should just let it be this way.

[serhiy-storchaka]

New changeset cd44afc by Serhiy Storchaka in branch 'main':
bpo-40296: Fix supporting generic aliases in pydoc (GH-30253)
cd44afc

[serhiy-storchaka]

New changeset a5b7678 by Serhiy Storchaka in branch '3.10':
[3.10] bpo-40296: Fix supporting generic aliases in pydoc (GH-30253). (GH-31976)
a5b7678

[serhiy-storchaka]

New changeset e207d72 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-40296: Fix supporting generic aliases in pydoc (GH-30253). (GH-31976) (GH-31981)
e207d72