编写程序并测试，有一个汽车类 Vehicle ，类中的私有数据成员为车轮个数 wheels 和车重 weight ：小车类 Car 是汽车类 vehicle 派生类 其中包含载客人数 passenger _ load ，默认4人；卡车类 Truck 是汽车类 vehicle 派生类，其中包含载客人数 passenger _ load 和载重量 payload 。 提示：编写类时要使用 get 和 set 方法， Vehicle 类定义 display (）显示车轮和重量， Car 和 Truck 中要对 display (）进行同名覆盖。

以下是Python代码实现：

class Vehicle:
    def __init__(self, wheels=4, weight=1000):
        self.__wheels = wheels
        self.__weight = weight

    def set_wheels(self, wheels):
        self.__wheels = wheels

    def set_weight(self, weight):
        self.__weight = weight

    def get_wheels(self):
        return self.__wheels

    def get_weight(self):
        return self.__weight

    def display(self):
        print("Wheels:", self.__wheels)
        print("Weight:", self.__weight)


class Car(Vehicle):
    def __init__(self, passenger_load=4):
        super().__init__()
        self.__passenger_load = passenger_load

    def set_passenger_load(self, passenger_load):
        self.__passenger_load = passenger_load

    def get_passenger_load(self):
        return self.__passenger_load

    def display(self):
        super().display()
        print("Passenger load:", self.__passenger_load)


class Truck(Vehicle):
    def __init__(self, passenger_load=2, payload=5000):
        super().__init__()
        self.__passenger_load = passenger_load
        self.__payload = payload

    def set_passenger_load(self, passenger_load):
        self.__passenger_load = passenger_load

    def set_payload(self, payload):
        self.__payload = payload

    def get_passenger_load(self):
        return self.__passenger_load

    def get_payload(self):
        return self.__payload

    def display(self):
        super().display()
        print("Passenger load:", self.__passenger_load)
        print("Payload:", self.__payload)


# 测试代码
car1 = Car()
car1.display()

car1.set_wheels(6)
car1.set_weight(1200)
car1.set_passenger_load(5)
car1.display()

truck1 = Truck()
truck1.display()

truck1.set_wheels(8)
truck1.set_weight(10000)
truck1.set_passenger_load(3)
truck1.set_payload(10000)
truck1.display()

输出结果如下：

Wheels: 4
Weight: 1000
Passenger load: 4
Wheels: 6
Weight: 1200
Passenger load: 5
Wheels: 4
Weight: 1000
Passenger load: 2
Payload: 5000
Wheels: 8
Weight: 10000
Passenger load: 3
Payload: 10000