Python class type usage before created

Question

I need class with possibility of create other class instances and self instances in class method scope. I have following code:

class A:
    #somme stuff

class B:
    allowed_children_types = [ #no reason to make self.allowed_children_types
        A,
        C #first problem, no C know
    ]

    @staticmethod
    def foo(self):
        #use allowed_children_types to create children objects


class C:
    allowed_children_types = [  # no reason to make self.allowed_children_types
        A,
        B
        C  # second problem, no C know because type object is not yet created
    ]

    @staticmethod
    def foo(self):
        #use allowed_children_types to create children objects

I will not create independent factory because it will complicated very simple application logic. I feel that create custom metaclass is usually bad designe.

What should I do to jump over this issue?

Answer 1

You have to have all those names defined before you use them. Something like:

class A:
    #somme stuff

class B:

    @staticmethod
    def foo(self):
        #use allowed_children_types to create children objects


class C:

    @staticmethod
    def foo(self):
        #use allowed_children_types to create children objects

B.allowed_children_types = [A, C]
C.allowed_children_types = [A, B, C]