Re: help(list[int]) → TypeError

[Julio Di Egidio]

On Thursday, 3 December 2020 at 19:28:19 UTC+1, Paul Bryan wrote:
> Is this the correct behavior? 
> 
> Python 3.9.0 (default, Oct 7 2020, 23:09:01) 
> [GCC 10.2.0] on linux 
> Type "help", "copyright", "credits" or "license" for more information. 
> >>> help(list[int]) 
> Traceback (most recent call last): 
> File "<stdin>", line 1, in <module> 
> File "/usr/lib/python3.9/_sitebuiltins.py", line 103, in __call__ 
> return pydoc.help(*args, **kwds) 
> File "/usr/lib/python3.9/pydoc.py", line 2001, in __call__ 
> self.help(request) 
> File "/usr/lib/python3.9/pydoc.py", line 2060, in help 
> else: doc(request, 'Help on %s:', output=self._output) 
> File "/usr/lib/python3.9/pydoc.py", line 1779, in doc 
> pager(render_doc(thing, title, forceload)) 
> File "/usr/lib/python3.9/pydoc.py", line 1772, in render_doc 
> return title % desc + '\n\n' + renderer.document(object, name) 
> File "/usr/lib/python3.9/pydoc.py", line 473, in document 
> if inspect.isclass(object): return self.docclass(*args) 
> File "/usr/lib/python3.9/pydoc.py", line 1343, 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 
> >>> 
> 
> I would have expected the output to the identical to help(list).

As I get it from the docs (*), these new generics still only work in type hinting contexts,
and I'd rather have expected a more useful error message: but, whether that is temporary
(possibly a plain bug, as in a forgotten case) or, instead, just "how things are", I wouldn't
know... might be a good question for Python developers.

(*) As in this one for a starter, but see also PEP 585:
"*In type annotations* you can now use ...", my emphasis.
<https://docs.python.org/3.9/whatsnew/3.9.html#type-hinting-generics-in-standard-collections>

Julio