Subclasses of typing.Sequence (&c) pretend to be superclasses of all registered members of abc.Sequence (&c) #268
Description
Check this out yo:
In [1]: from typing import Sequence
In [2]: class DumbSeq(Sequence): pass
In [3]: issubclass(tuple, DumbSeq)
Out[3]: True
This has to do with the implementation of GenericMeta, where our __subclasscheck__ ends with this line:
return issubclass(cls, self.__extra__)And for the container classes in typing, they're defined to have the collections.abc classes as their __extra__.
Pondering a fix to suggest.