Inheriting function type hints from child class

Question

Is there a way to make a generic class A[T], which has a function that inherits the type for the same function in T?

I want to make something like these 2 classes:

class A[T]:
    ...
    def a(self):
        ...

class B(A):
    def a(self, a: int, b:int):
        ...

and have A[B].a's type be (self: B, a: int, b: int) -> None, instead of (self: A) -> None. Is there a way to do this without repeating the type hints in the definition of the B class?

FYI that breaks the LSP; def demo(a: A): return a.a() fails for demo(B()), because the subclass method has required arguments the superclass method does not.. — jonrsharpe
– jonrsharpe, Commented Sep 19 at 11:03
(a quick workaround is to make the arguments non-mandatory, thanks to default values) — globglogabgalab
– globglogabgalab, Commented Sep 19 at 11:13
What does the base class definition do? Does it need the extra arguments? If you need to say the type is A[B] – "this is sort of an A, but you can't use it without knowing it's really a B" – then it might be clearer to make the base class method a "private" helper with a different name, and have the static type of your object be the concrete type B. — David Maze
– David Maze, Commented Sep 19 at 11:23
It's unclear what you mean by A[B] - A doesn't currently use T, and why would that be its own subclass? Maybe you want something like this, but note that tells you the same thing for this specific case: B's implementation of a is not compatible with the supertype. — jonrsharpe
– jonrsharpe, Commented Sep 19 at 12:53
This is clearly a legitimate question, and the O.P. needs to be taught about what is expected in inheritance, and LSP in the answer. I don't think this should be closed at all - least why "the O.P. have the wrong premises" - that is what the answers are supposed to tackle. — jsbueno
– jsbueno, Commented Sep 21 at 15:36

Marce Puente · Accepted Answer · 2025-09-19 12:43:55Z

-1

I'm not sure if this is what you need, but you can leave out the generic class and make the method in question generic, something like:

from typing import TypeVar

T = TypeVar('T')

class A():
    
    def a( self, st : T ):
        print( f" hello user {st}" )

class B( A ):
    pass

    
objectA = A()
objectA.a( "What are they?!" )
objectB = B()
objectB.a( 118 )

answered Sep 19 at 12:43

Marce Puente

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