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9-9 电瓶升级

1. 项目

在本节最后一个 electric_car.py 版本中，给 Battery 类添加一个名为upgrade_battery()的方法。这个方法检查电瓶容量，如果它不是 85，就将它设置为 85。

创建一辆电瓶容量为默认值的电动汽车，调用方法 get_range()，然后对电瓶进行升级，并再次调用 get_range()。

你会看到这辆汽车的续航里程增加了。

2. 代码

class Car():
 
    def __init__(self, make, model, year):
        """初始化描述汽车的属性"""
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0
 
    def get_descriptive_name(self):
        """返回整洁的描述性信息"""
        long_name = str(self.year) + ' ' + self.make + ' ' + self.model
        return long_name.title()
 
    def update_odometer(self, mileage):
        """将里程表读数设置为指定的值"""
        """
        将里程表读数设置为指定的值
        禁止将里程表读数往回调
        """
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You can't roll back an odometer!")
 
    def increment_odometer(self, miles):
        """将里程表读数增加指定的量"""
        self.odometer_reading += miles
 
    def read_odometer(self):
        """打印一条指出汽车里程的消息"""
        print("This car has " + str(self.odometer_reading) + " miles on it.")
 
class Battery():
    """一次模拟电动汽车电瓶的简单尝试"""
 
    def __init__(self, battery_size=70):
        """初始化电瓶的属性"""
        self.battery_size = battery_size
 
    def describe_battery(self):
        """打印一条描述电瓶容量的消息"""
        print("This car has a " + str(self.battery_size) + "-kWh battery.")
 
    def upgrade_battery(self):
        if self.battery_size != 85:
            self.battery_size =85
 
    def get_range(self):
        """打印一条消息， 指出电瓶的续航里程"""
        if self.battery_size == 70:
            range = 240
        elif self.battery_size == 85:
            range = 270
 
        message = "This car can go approximately " + str(range)
        message += " miles on a full charge."
        print(message)
 
class ElectricCar(Car):
    """电动车的独特之处"""
 
    def __init__(self, make, model, year):
        """
        初始化父类的属性，再初始化电动汽车特有的属性
        """
        super().__init__(make, model, year)
        self.battery = Battery()
 
 
my_tesla = ElectricCar('tesla', 'model X', 2021)
my_tesla.battery.get_range()
 
my_tesla.battery.upgrade_battery()
my_tesla.battery.get_range()