Python :在子类中设置变量

Question

通过初级课程学习Python，目前正在上课。作为一个例子，这本书是用汽车/电动汽车的描述来解释类和子类等等。

以下是代码：

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()

在类电池()中，方法get_range显示两个可能的电池大小(70和85)，以及它们各自的范围。

在电池的init中，电池的大小默认设置为70 kWh。

我如何调用电池()将电池大小设置为85 kWh的车辆？

Answer 1

只要给它一个价值：

self.battery = Battery(85)

只有在没有传递给函数的值时才使用默认值，否则将使用传递的参数。

正如@jasonharper所建议的，您可以在ElectricCar的__init__()方法中添加一个参数，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)