Say I have an abstract class:
class A(metaclass=ABCMeta):
def __init__(self):
pass
@abstractmethod
def a_function(self) -> int:
return 0
I want to constrain the type of the output of a_function so that when a class inherits from A the output has to be an integer.
My first attempt was to make a decorator for a_function of class A (see below). But of course it only constrains A.a_function
def constrain_type(f):
def decorated(*args, **kwargs):
output = f(*args, **kwargs)
class_annotation = f.__annotations__["return"]
if not issubclass(type(output), class_annotation):
raise TypeError("this class must return an object inheriting from " +
class_annotation.__name__ + " not " + type(output).__name__)
return output
return decorated
