several articles to explain how python metaclass works

meta.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author: Liu Yuande
# https://jakevdp.github.io/blog/2012/12/01/a-primer-on-python-metaclasses/
# http://stackoverflow.com/questions/100003/what-is-a-metaclass-in-python
# http://stackoverflow.com/questions/17801344/python-understanding-metaclass-and-inheritance

# give a name, create a new car class. define the class in a more dynamic way.
# classes can inherit properties from parents and add or specialize attributes and methods.

# classes are objects, and they are objects of type type. type is a metaclass: a class which instantiates classes. All new-style classes in Python are instances of the type metaclass, including type itself. type is an instance of itself.

import random

class CarBase(object):
    pass

class meta_car(type):
    car_brands = {}
    def __init__(cls, cls_name, cls_bases, cls_dict):
        super(meta_car, cls).__init__(cls_name, cls_bases, cls_dict)
        if(not CarBase in cls_bases):
            meta_car.car_brands[cls_name] = cls

    def __call__(self, *args, **kwargs):
        make = kwargs.get("make", "")
        if meta_car.car_brands.has_key(make) and not (self is meta_car.car_brands[make]):
            obj = meta_car.car_brands[make].__call__(*args, **kwargs)
            if(make == "Toyota"):
                if(random.randint(0, 100) < 2):
                    obj.defect = "sticky accelerator pedal"
            elif(make == "GM"):
                if(random.randint(0, 100) < 20):
                    obj.defect = "shithouse"
            elif(make == "Great Wall"):
                if(random.randint(0, 100) < 101):
                    obj.defect = "cancer"
        else:
            obj = None
            if not meta_car.car_brands.has_key(self.__name__):
                new_class = meta_car(make, (GenericCar,), {})
                globals()[make] = new_class
                obj = new_class(*args, **kwargs)
            else:
                obj = super(meta_car, self).__call__(*args, **kwargs)
        return obj

class Car(CarBase):
    __metaclass__ = meta_car

    def __init__(self, **kwargs):
        for name, value in kwargs.items():
            setattr(self, name, value)

    def __repr__(self):
        return "<%s>" % self.description

    @property
    def description(self):           
        return "%s %s %s %s" % (self.color, self.year, self.make, self.model)

class GenericCar(Car):
    def __init__(self, **kwargs):
        kwargs["make"] = self.__class__.__name__
        super(GenericCar, self).__init__(**kwargs)

class Toyota(GenericCar):
    pass

colours = \
[
    "blue",
    "green",
    "red",
    "yellow",
    "orange",
    "purple",
    "silver",
    "black",
    "white"
]

def rand_colour():
    return colours[random.randint(0, len(colours) - 1)]

some_cars = \
[
    Car(make="Toyota", model="Prius", year=2005, color=rand_colour()),
    Car(make="Toyota", model="Camry", year=2007, color=rand_colour()),
    Car(make="Toyota", model="Camry Hybrid", year=2013, color=rand_colour()),
    Car(make="Toyota", model="Land Cruiser", year=2009, color=rand_colour()),
    Car(make="Toyota", model="FJ Cruiser", year=2012, color=rand_colour()),
    Car(make="Toyota", model="Corolla", year=2010, color=rand_colour()),
    Car(make="Toyota", model="Hiace", year=2006, color=rand_colour()),
    Car(make="Toyota", model="Townace", year=2003, color=rand_colour()),
    Car(make="Toyota", model="Aurion", year=2008, color=rand_colour()),
    Car(make="Toyota", model="Supra", year=2004, color=rand_colour()),
    Car(make="Toyota", model="86", year=2013, color=rand_colour()),
    Car(make="GM", model="Camaro", year=2008, color=rand_colour())
]

dodgy_vehicles = filter(lambda x: hasattr(x, "defect"), some_cars)
print dodgy_vehicles