python入门（七）计算不同交通工具的行进耗时（类的用法和继承）

class Vehicle:
    def __init__(self, speed = 60.0):
        self.speed = speed
        #下一个函数需要这个值

    def drive(self, distance):
        print("need %f hour" % (distance / self.speed))


class Bike(Vehicle):
    pass


class Car(Vehicle):
    def __init__(self, speed, fuel):
        Vehicle.__init__(self, speed)
        self.fuel = fuel


    def drive(self, distance):
        Vehicle.drive(self, distance)
        print("need %f fuels" % (distance * self.fuel))


b = Bike(15.0)
c = Car(80.0, 0.012)
b.drive(100.0)
c.drive(100.0)