Allan Daemon <rea....@gmail.com> added the comment:
> I actually have no idea where dir() gets its information.
I will share what I find out already, so it may hopefully be helpful.
The dir function used is the general object.__dir__ function, defined in
Objects/typeobject.c:type___dir___impl(), that just takes everything from
__dict__ of the class and its bases.
But the GenericAlias is trying hard pretending to be the origin class, so when
you ask for the __dict__, it gives the original class, not the GenericAlias:
>>> list[int].__dict__ == list.__dict__
True
There are also some other things that seems a bit strange, but it may just be
right:
>>> list.__class__
<class 'type'>
>>> list[int].__class__
<class 'type'>
>>> type(list)
<class 'type'>
>>> type(list[int])
<class 'types.GenericAlias'>
This happens because of the tp_getattro function
genericaliasobject.c:ga_getattro(), that takes the attributes from the origin
except for the following names, that are taken from the GenericAlias itself:
"__origin__",
"__args__",
"__parameters__",
"__mro_entries__",
"__reduce_ex__",
"__reduce__",
So, when the dir() is getting the __dict__, it gets list.__dict__ and base
(object) instead of GenericAlias. Looking the ga_getattro() calls when dir() is
fired, it also gets the __class__ attribute after getting the __dict__. Adding
one or another makes the dir() showing up the GenericAlias attributes, but
others went missing.
An idea to solve this spefic issue could be overriding the __dir__ method,
something like this python code (written in c, of course):
def __dir__(self):
r = super().__dir__()
return r + attribute_names_list + method_names_list
But I wonder what else should not be forwarded to origin.
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components: +Interpreter Core -Documentation, Library (Lib)
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue41780>
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