类中将实例对象作为一个属性

class Car():
  def __init__(self, make, model, year):
     self.make = make
     self.model = model
     self.year = year
     self.odometer_reading = 0
  def get_descriptive_name(self):
     long_name = '产自'+str(self.year) + '年' + self.make + ' ' + self.model
     return long_name.title()

  def read_odometer(self):
     print("This car has " + str(self.odometer_reading) + " miles on it.")

  def update_odometer(self, mileage):
     if mileage >= self.odometer_reading:
       self.odometer_reading = mileage
     else:
       print("You can't roll back an odometer!")
  def increment_odometer(self, miles):
       self.odometer_reading += miles
  def fill_gas_tank(self):
       print("XXXXXXXXXXXXXXXxx")

class Battery():
  def __init__(self, battery_size=70):
      self.battery_size = battery_size
  def describe_battery(self):
      print("This car has a " + str(self.battery_size) + "-kWh battery.")
  def  set_battery(self,battery_size):
      self.battery_size=battery_size          --------------------创建电瓶对象

class ElectricCar(Car):
  def __init__(self, make, model, year):
      super().__init__(make, model, year)
      self.battery=Battery()--------------------->这行代码让Python创建一个新的Battery实例（由于没有指定尺寸，因此为默认值70），并将该实例存储在属性self.battery中。每当方法__init__()被调用时，都将执行该操作；因此现在每个ElectricCar实

例都包含一个自动创建的Battery实例。

  def fill_gas_tank(self):
      print("This car doesn't need a gas tank!")


myCar=ElectricCar('audo','A6L',2020)
print(myCar.get_descriptive_name())
myCar.battery.describe_battery()------->这行代码让Python在实例myCar中查找属性battery，并对存储在该属性中的Battery实例调用方法describe_battery()

myCar.battery.set_battery(100)------->调用属性中的方法
myCar.battery.describe_battery()
myCar.fill_gas_tank()