[Python] Is there a way to annotate a function with two generic arguments indicating that both...

I would like to write a function accepting two arguments that are supposed to be compatible with the same base class:

def example_function(base_object: RelatedType, desired_type: type[DesiredType]) -> DesiredType:
...


where RelatedType and DesiredType should be generics bound to the same parent class (which is known only when the function is called with concrete arguments).

I understand inheritance relationship cannot be enforced between different generics, i.e. something like:

BaseType = TypeVar("BaseType")
DerivedType = TypeVar("DerivedType", bound=BaseType)


because a generic cannot be an upper bound.

What is the correct way to provide meaningful type hints that convey the intended relationship?

Continue reading...