Python Factory Using a Metaclass

MetaFactory.py

# https://stackoverflow.com/a/5961102
# Note python3 has a different declaration than the so post

class ShapeFactory(type):
    """Shape Factory"""

    def __call__(cls, selector, *args):
        if cls is Shape:
            # select a new object
            print('factory build:', selector)
            if selector == 'rectangle': return Rectangle(selector, *args)
            if selector == 'triangle': return Triangle(selector, *args)
            raise 'unrecognized shape'

        # And initialize it
        print('factory initialize:', selector)
        return type.__call__(cls, selector, *args)

class Shape(metaclass=ShapeFactory):
    """Base Shape object.  Contains factory and common methods"""

    def __init__(self, selector, name):
        """

        Args:
            selector: The type of shape to build.
            name: The second parameter.

        Returns:
            Nothing.
        """

        print("shape init")
        self.desc = name
        self.edge_count = None

        return

    @property
    def number_of_edges(self):
        return self.edge_count


class Triangle(Shape):
    def __init__(self, selector, name):
        print("triangle init: {}".format(name))

        super().__init__(selector, name)
        self.edge_count = 3
        return

    @property
    def name(self):
        return 'Triangle'


class Rectangle(Shape):
    def __init__(self, selector, name):
        print("rectangle init: {}".format(name))

        super().__init__(selector, name)
        self.edge_count = 4

        return

    @property
    def name(self):
        return 'Rectangle'

if __name__ == '__main__':
    shape = Shape('rectangle', 'big')
    print('{} has {} edges'.format(shape.name, shape.number_of_edges))

    print()
    shape = Triangle('rectangle', 'junk')
    print('{} has {} edges'.format(shape.name, shape.number_of_edges))