Class variable in multiple base classes incompatible

[jeremander]

I'm getting a mypy error when I inherit from multiple base classes which define the same class variable.

A minimal script looks like:

class Obj:
    ...

class Left(Obj):
    ...

class Right(Obj):
    ...

class A:
    val: Obj

class B(A):
    val = Left()

class C(A):
    val = Right()

class D(B, C):
    ...

The error I get is:

Definition of "val" in base class "B" is incompatible with definition in base class "C"  [misc]

I was expecting there to be no error here. The following script works, for instance:

class Obj:
    ...

class Left(Obj):
    ...

class Right(Obj):
    ...

val: Obj
val = Left()
val = Right()

I can avoid the error by changing the definitions of B and C to:

class B(A):
    val: Obj = Left()

class C(A):
    val: Obj = Right()

But this seems redundant.

Environment

• Mypy version used: 1.9.0
• Mypy command-line flags: None
• Python version used: 3.11