[英]Python Beginner: Setting a variable in a subclass
Working through a beginner course to Python and currently on classes. 通过初学者课程学习Python,目前正在上课。 As an example, the book is using descriptions of Cars/Electric cars to explain classes and sub-classes, etc.
作为一个例子,本书使用汽车/电动汽车的描述来解释课程和子课程等。
Here is the code: 这是代码:
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()
In the class Battery(), the method get_range shows two possible battery sizes (70 and 85), along with their respective ranges. 在类Battery()中,方法get_range显示两种可能的电池尺寸(70和85)及其各自的范围。
In the init for Battery, the battery size is by default set to 70 kWh. 在电池初始化中,电池尺寸默认设置为70 kWh。
How would I call on Battery() to set the battery size to 85 kWh for a vehicle? 我如何打电话给Battery()将车辆的电池尺寸设置为85 kWh?
Just give it the value: 只要赋予它价值:
self.battery = Battery(85)
The default values are used only when there are no values passed into the function, otherwise, the arguments that are passed are used. 仅当没有值传递给函数时才使用默认值,否则使用传递的参数。
And as @jasonharper suggested, you can add a parameter to the ElectricCar
's __init__()
method that specifies the battery size: 正如@jasonharper建议的那样,你可以在
ElectricCar
的__init__()
方法中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)
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