Example of Python's __new__ used in conjunction with inheritance

Python - Inheritance and new.py

import sys


class Root:

    # Derived class references.
    # As the classes Alpha and Beta are not already defined, their names are
    # stored instead of their reference ("Alpha" instead of Alpha).
    __derived = {
        "alpha": {"class": "Alpha", "count": 0},
        "beta":  {"class": "Beta",  "count": 0}
    }

    def __new__(cls, derived_name, *args, **kwargs):
        print("Root.__new__(cls={}, derived_name={}, *args={})".format(cls, derived_name, args))
        if derived_name in cls.__derived:
            cls.__derived[derived_name]["count"] += 1
            return object.__new__(getattr(sys.modules[__name__], cls.__derived[derived_name]["class"]))
        else:
            raise Exception("Invalid derived_name. Requires one of {}".format(", ".join(data.keys())))

    def __init__(self, token, *args, **kwargs):
        print("Root.__init__(self={}, token={})".format(self, token))
        self.token = token

    @classmethod
    def count(cls, derived_name):
        return cls.__derived[derived_name]["count"]


class Alpha(Root):
    def __init__(self, *args):
        print("Alpha.__init__(self={}, *args={})".format(self, args))
        super().__init__("alpha_token")

    def foo(self):
        print("Alpha.foo(): token = {}".format(self.token))


class Beta(Root):
    def __init__(self, *args):
        print("Beta.__init__(self={}, *args={})".format(self, args))
        super().__init__("beta_token")

    def foo(self):
        print("Beta.foo(): token = {}".format(self.token))


if __name__ == "__main__":
    i, j = Root("alpha"), Root("beta")
    i.foo()
    j.foo()
    print("alphas: {}".format(Root.count("alpha")))
    print("betas:  {}".format(Root.count("beta")))