generic subclasss and typevar with constraint

Not sure if this is a "bug" or I didn't understand generics, but

import typing

T = typing.TypeVar('T', str, int)


class Base(typing.Generic[T]):

    def __init__(self, bar: T):
        self.bar: T = bar


class Child(Base[T]):

    def __init__(self, bar: T):
        super().__init__(bar)

mypy 0.720 (on windows) says

> mypy.exe test\__init__.py
test\__init__.py:15: error: Argument 1 to "__init__" of "Base" has incompatible type "str"; expected "T"
test\__init__.py:15: error: Argument 1 to "__init__" of "Base" has incompatible type "int"; expected "T"

but if I change the T definition to T = typing.TypeVar('T') the errors go away

What I want is to specify that

• the "Base" constructor has a parameter that could be an int or a str
• the "Child" constructor has the same "signature" of the "Base" one (well, this is a simplified example, I want something more...)

is this a bug? di I misinterpreted the TypeVar usage?

Reproduce the example in test_init_.py with mypy 0.720, comparing the constrained TypeVar with the unconstrained version. Read the relevant generic and TypeVar-checking paths, then establish whether the reported diagnostic is expected; done means documenting the behavior or adding a regression test and correcting it if it is a bug.