Object-oriented demonstration for SO question http://stackoverflow.com/q/9237725/307705

cars.py

import random

class Vehicle(object):
    def __init__ (self, _id):
        self.company = None
        self.id = _id

    def printDoors(self):
        print 'Car ' + str(self.id) + ' has ' + str(self.doors) + ' doors.'

    def findSameDoors(self):
        for i in self.company.cars:
            if self.id != i.id and self.doors == i.doors:
                print 'Car ' + str(i.id) + ' does too!'

class Sedan(Vehicle):
    name = 'sedan'
    doors = 4

class Convertible(Vehicle):
    name = 'convertible'
    doors = 2

class Motorcycle(Vehicle):
    name = 'motorcycle'
    doors = 0

class Company(object):
    def __init__ (self, name, types):
        self.name = name
        self.types = types
        self.cars = []

    def add_vehicle(self, vehicle):
        self.cars.append(vehicle)
        vehicle.company = self

porsche = Company('Porsche', [Sedan, Convertible])
honda = Company('Honda', [Sedan, Convertible, Motorcycle])

for i in range(10):
    vehicle_class = random.choice(porsche.types)
    porsche.add_vehicle(vehicle_class(i))

for i in range(10):
    vehicle_class = random.choice(honda.types)
    honda.add_vehicle(vehicle_class(i))


porsche.cars[0].printDoors()
porsche.cars[0].findSameDoors()