class Car(object):
    __slots__ = ("color", "gastank", "engine")
    
    def __init__(self):
        self.color = "red"
        self.gastank = Tank(100)
        self.engine = Engine()

class Engine(object):
    __slots__ = ("horsepower")
    
    def __init__(self):
        horsepower = 9001

class Tank(object):
    __slots__ = ("percent_gas_remaining")
    
    def __init__(self, percent_left):
        self.percent_gas_remaining = percent_left