Python初學者：在子類中設置變量

Question

通過初學者課程學習Python，目前正在上課。 作為一個例子，本書使用汽車/電動汽車的描述來解釋課程和子課程等。

這是代碼：

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()

在類Battery（）中，方法get_range顯示兩種可能的電池尺寸（70和85）及其各自的范圍。

在電池初始化中，電池尺寸默認設置為70 kWh。

我如何打電話給Battery（）將車輛的電池尺寸設置為85 kWh？

Answer 1

只要賦予它價值：

self.battery = Battery(85)

僅當沒有值傳遞給函數時才使用默認值，否則使用傳遞的參數。

正如@jasonharper建議的那樣，你可以在ElectricCar的__init__()方法中添加一個參數來指定電池大小：

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