mypy not flagging subclasses with incompatible constructors

reproducer

from typing import Type
class Foo:
    def __init__(self, a):
        self.a = a

class Bar(Foo):
    def __init__(self):
        super().__init__("Bar")


def takes_foo(foo: Type[Foo]):
    x = foo("Foo")


takes_foo(Foo)
takes_foo(Bar)

observed behavior
mypy raises no errors, but the code raises a TypeError at runtime.

expected behavior
pep 484 states:

when new_user() calls user_class() this implies that all subclasses of User must support this in their constructor signature...A type checker ought to flag violations of such assumptions, but by default constructor calls that match the constructor signature in the indicated base class (User in the example above) should be allowed.

My understanding of the above is that mypy should be raising an error on the Bar definition because its signature is incompatible with that of its superclass. More generally, I tend to be surprised when code that passes mypy raises a TypeError at runtime.

environment
master as of 2019-06-10

$ pipenv graph
mypy==0.710+dev.e2f31ed71bd1edd60bffc86d3fda9da15ba63b3d
  - mypy-extensions [required: >=0.4.0,<0.5.0, installed: 0.4.1]
  - typed-ast [required: >=1.4.0,<1.5.0, installed: 1.4.0]
$ pipenv run python --version
Python 3.7.3

Thank you all for an amazing tool!

Commencez par le reproducer de l’issue et comparez son comportement avec les recommandations de PEP 484 concernant les constructeurs et les objets de classe. Étudiez la manière dont mypy gère les signatures de constructeur des sous-classes et déterminez si le résultat attendu est une erreur sur Bar ou sur takes_foo(Bar). C’est terminé lorsque le comportement est couvert par un test de régression et que le checker signale l’incompatibilité attendue.