>>> 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

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

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.

New changeset cd44afc573e2e2de8d7e5a9119c347373066cd10 by Serhiy Storchaka in branch 'main':
bpo-40296: Fix supporting generic aliases in pydoc (GH-30253)
https://github.com/python/cpython/commit/cd44afc573e2e2de8d7e5a9119c347373066cd10

New changeset a5b7678a67ac99edd50822827b772e7d9afc8e64 by Serhiy Storchaka in branch '3.10':
[3.10] bpo-40296: Fix supporting generic aliases in pydoc (GH-30253). (GH-31976)
https://github.com/python/cpython/commit/a5b7678a67ac99edd50822827b772e7d9afc8e64

New changeset e207d721fcea01123f0e3edb83b6decdcb5e5e63 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-40296: Fix supporting generic aliases in pydoc (GH-30253). (GH-31976) (GH-31981)
https://github.com/python/cpython/commit/e207d721fcea01123f0e3edb83b6decdcb5e5e63