Python初学者: Setting a variable in a subclass

Question

正在学习 Python 初学者类(class)，目前正在上课。例如，本书使用汽车/电动汽车的描述来解释类和子类等。

代码如下:

class Car():
    ''' A simple attempt to represent a car ''' 

    def __init__(self, make, model, year):
        ''' Initialize attributes to describe a car '''
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0

    def car_description(self):
        ''' Return a neatly formatted descriptive name '''
        long_name = str(self.year) + ' ' + self.make + ' ' + self.model
        return long_name.title()

class ElectricCar(Car):
    # When we put (Car) in the class definition, a child class is created with the attributes of Car.
    ''' Represents aspects of a car, specific to electric vehicles. ''' 

    def __init__(self, make, model, year):
        ''' Initalize attributes of the parent class. '''
        super().__init__(make,model,year)
        self.battery = Battery()

class Battery():
    ''' A simple attempt to model a battery for an electric car. '''

    def __init__(self, battery_size=70):
        ''' Initialize the battery's attributes.'''
        self.battery_size = battery_size

    def describe_battery(self):
        ''' Print a statement describing the battery size. ''' 
        print("This car has a " + str(self.battery_size) + "-kWh battery.")

    def get_range(self):
        ''' Print a statement about the range this battery provides. '''
        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)

my_tesla = ElectricCar('tesla','model s', 2016)
print(my_tesla.car_description())
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()

在 Battery() 类中，方法 get_range 显示两种可能的电池大小(70 和 85)以及它们各自的范围。

在电池的init中，电池容量默认设置为 70 kWh。

如何调用 Battery() 将车辆的电池容量设置为 85 kWh？

Answer 1

只需给它一个值:

self.battery = Battery(85)

仅当没有值传递到函数中时才使用默认值，否则使用传递的参数。

正如 @jasonharper 建议的那样，您可以向 ElectricCar 的 __init__() 方法添加一个参数来指定电池大小:

def __init__(self, make, model, year, batterySize):
    ''' Initalize attributes of the parent class. '''
    super().__init__(make,model,year)
    self.battery = Battery(batterySize)