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Author AllanDaemon
Recipients AllanDaemon, BTaskaya, docs@python, gvanrossum
Date 2020-09-15.11:35:58
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> 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__

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:

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.
Date User Action Args
2020-09-15 11:35:58AllanDaemonsetrecipients: + AllanDaemon, gvanrossum, docs@python, BTaskaya
2020-09-15 11:35:58AllanDaemonsetmessageid: <>
2020-09-15 11:35:58AllanDaemonlinkissue41780 messages
2020-09-15 11:35:58AllanDaemoncreate