If you really want types, use classes. It removes the need for single dispatch, creates a self documenting namespace and saves you an import when you want to do the calculation.

    import math
    from dataclasses import dataclass

    @dataclass
    class Rectangle:
        length: int
        breadth: int
        def area(self) -> int:
            return self.length * self.breadth

    @dataclass
    class Circle:
        radius: int
        def area(self) -> float:
            return math.pi * self.radius ** 2

We are talking about very simple things here. No need to add complexity to them.