Bad self type inference with Generics and inheritance?

• Are you reporting a bug, or opening a feature request?

Reporting a bug

• Please insert below the code you are checking with mypy

from typing import TypeVar, Generic

T = TypeVar("T")

class Foo(Generic[T]):
    def __init__(self): ...

class Bar(Generic[T]): ...

class FooChild(Foo[Bar[T]]):
    def __init__(self, blah: T):
        Foo.__init__(self)

• What is the actual behavior/output?

$ mypy foo.py
foo.py:18: error: Argument 1 to "__init__" has incompatible type "FooChild[T]"; expected "Foo[T]"
Found 1 error in 1 file (checked 1 source file)

• What is the behavior/output you expect?

Success: no issues found in 1 source file

• What are the versions of mypy and Python you are using?

mypy 0.750
Python 3.7.3

• Do you see the same issue after installing mypy from Git master?

Yes, successfully reproduced with mypy 0.790+dev.df6894b5a9bb1a913e66df87138cd7a240c09fc1

• What are the mypy flags you are using? (For example --strict-optional)

No flags.

• If mypy crashed with a traceback, please paste
  the full traceback below.

No crash

• Additional information:

The following versions typecheck successfully:

from typing import TypeVar, Generic

T = TypeVar("T")

class Foo(Generic[T]):
    def __init__(self): ...

class Bar(Generic[T]): ...

class FooChild(Foo[T]): # Removed one level of nesting here
    def __init__(self, blah: T):
        Foo.__init__(self)

from typing import TypeVar, Generic

T = TypeVar("T")

class Foo(Generic[T]):
    def __init__(self): ...

class Bar(Generic[T]): ...

class FooChild(Foo[Bar[T]]):
    def __init__(self): # Removed the argument here
        Foo.__init__(self)

Inizia con il riproduttore foo.py fornito ed eseguilo con le versioni di mypy indicate, confermando il tipo self errato per FooChild[T]. Traccia l’ereditarietà generica e la chiamata al costruttore coinvolte nell’inferenza dei tipi di mypy, quindi aggiungi una copertura che dimostri che il caso annidato Bar[T] ha esito positivo senza errori.