class FactoryMetaclassObject(type):

    def __init__(cls, name, bases, attrs):
        """__init__ will happen when the metaclass is constructed: 
        the class object itself (not the instance of the class)"""
pass

def __call__(*args, **kw):
    """
        __call__ will happen when an instance of the class (NOT metaclass)
        is instantiated. For example, We can add instance methods here and they will
        be added to the instance of our class and NOT as a class method
        (aka: a method applied to our instance of object).
        Or, if this metaclass is used as a factory, we can return a whole different
        classes' instance
        """
return 'hello world!'


class FactorWorker(object, metaclass=FactoryMetaclassObject):
    pass
f = FactorWorker()
print(f.__class__)
Implementing the factory design pattern using metaclasses in python