Seehttp://bugs.python.org/issue26391 .

"""
A specialized sub-class of a generic type never calls__init__ when it is instantiated. See below for an example:

fromtypingimportGeneric,TypeVarT=TypeVar('T')classFoo(Generic[T]):def__init__(self,value:T):self.value=valueBar=Foo[str]foo=Foo('foo')bar=Bar('bar')print(type(foo),end=' ')print(foo.value)print(type(bar),end=' ')print(bar.value)# AttributeError

I would expect Foo[str], Foo[int], etc to be equivalent to Foo at run-time. If this is not the case it might deserve an explicit mention in the docs. At the moment, behaviour is confusing because an instance of Foo is returned that does not have any of its attributes set.
"""