python（18）类（2）

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　　==================================1.继承
　　编写类时，并非总是要从空白开始，如果要编写的类时一个现成类的特殊版本，可使用继承
　　一个类继承另一个类时，将自动获得另一个类的所有属性和方法；原有的类称为父类，新类称为子类。
　　子类继承了父类的所有属性和方法，同时还可以定义自己的属性和方法  ###1.子类的方法__init__（） #模拟电动汽车，电动汽车是一种特殊的汽车，因此可以在前面创建的Car()类基础上创建新的ElectricCar,这样就只需为电动汽车特有的属性和行为编写代码 class Car():          def __init__(self, make, model, year):         #一次模拟汽车的简单尝试         self.make = make         self.model = model         self.year = year         self.odometer_reading = 0     def get_descriptive_name(self):         long_name = str(self.year) + ＂ ＂ + self.make + ＂ ＂ + self.model         return long_name     def read_odometer(self):         print(＂this car has ＂ + str(self.odometer_reading) + ＂ miles on it＂)     def update_odometer(self, mileage):         if mileage >= self.odometer_reading:             self.odometer_reading = mileage         else:             print(＂you can not roll back an odometer＂)     def increment_odometer(self, miles):         self.odometer_reading += miles          class ElectricCar(Car):#创建一个子类，继承父类     #电动车的独特之处          def __init__(self, make, model, year):#接受父类的信息         #初始化父类的属性,super()函数帮助关联父类和子类         super(). __init__(make, model, year)  my_tesla = ElectricCar(＂tesla＂, ＂model s＂, 2016) print(my_tesla.get_descriptive_name()) 2016 tesla model s =============================================== ###2.给子类定义属性和方法 class Car():          def __init__(self, make, model, year):         #一次模拟汽车的简单尝试         self.make = make         self.model = model         self.year = year         self.odometer_reading = 0     def get_descriptive_name(self):         long_name = str(self.year) + ＂ ＂ + self.make + ＂ ＂ + self.model         return long_name     def read_odometer(self):         print(＂this car has ＂ + str(self.odometer_reading) + ＂ miles on it＂)     def update_odometer(self, mileage):         if mileage >= self.odometer_reading:             self.odometer_reading = mileage         else:             print(＂you can not roll back an odometer＂)     def increment_odometer(self, miles):         self.odometer_reading += miles          class ElectricCar(Car):#创建一个子类，继承父类     #电动车的独特之处          def __init__(self, make, model, year):#接受父类的信息         #初始化父类的属性,super()函数帮助关联父类和子类         super(). __init__(make, model, year)         self.battery_size = 70#给子类定义属性     def describe_battery(self):#给子类定义方法         #打印一条描述电池容量的消息         print(＂this car has ＂ + str(self.battery_size) + ＂-kwh battery＂)  my_tesla = ElectricCar(＂tesla＂, ＂model s＂, 2016) print(my_tesla.get_descriptive_name()) my_tesla.describe_battery() 2016 tesla model s this car has 70-kwh battery ==================================================== ###3.重写父类的方法 #对于父类的方法，只要它不符合子类模拟的实物的行为，都可对其重写。为此，可在子类中定义一个与要重写的父类方法同名，python将不会考虑父类方法，只关注子类中定义的相应方法 #假设Car类有一个名为fill_gas_tank()的方法，对电动车来说毫无意义，需要重新改写 class ElectricCar(Car):     --snip--          def fill_gas_tank():         #电动汽车没有油箱         print(＂this car does not need a gas tank＂) ================================================ ###4.将实例用作属性，将类的一部分作为一个独立的类提取出来 class Car():          def __init__(self, make, model, year):         #一次模拟汽车的简单尝试         self.make = make         self.model = model         self.year = year         self.odometer_reading = 0     def get_descriptive_name(self):         long_name = str(self.year) + ＂ ＂ + self.make + ＂ ＂ + self.model         return long_name     def read_odometer(self):         print(＂this car has ＂ + str(self.odometer_reading) + ＂ miles on it＂)     def update_odometer(self, mileage):         if mileage >= self.odometer_reading:             self.odometer_reading = mileage         else:             print(＂you can not roll back an odometer＂)     def increment_odometer(self, miles):         self.odometer_reading += miles           class Battery():#定义一个名为Battery的新类     #模拟电动车的简单尝试     def __init__(self, battery_size = 70):     #初始化电瓶属性         self.battery_size = battery_size          def describe_battery(self):#给子类定义方法         #打印一条描述电池容量的消息         print(＂this car has ＂ + str(self.battery_size) + ＂-kwh battery＂)          class ElectricCar(Car):#创建一个子类，继承父类     #电动车的独特之处          def __init__(self, make, model, year):#接受父类的信息         #初始化父类的属性,super()函数帮助关联父类和子类         super(). __init__(make, model, year)         self.battery = Battery()#添加一个名为self.battery的属性，并将Battery()实例存储在属性self.battery中           my_tesla = ElectricCar(＂tesla＂, ＂model s＂, 2016) print(my_tesla.get_descriptive_name()) my_tesla.battery.describe_battery() 2016 tesla model s this car has 70-kwh battery 2.导入类
　　python允许将类存储在模块中，然后在主程序中导入所需的模块  ###1.导入单个类 #创建一个Car()类，存储在car.py的模块中 class Car():          def __init__(self, make, model, year):         #一次模拟汽车的简单尝试         self.make = make         self.model = model         self.year = year         self.odometer_reading = 0     def get_descriptive_name(self):         long_name = str(self.year) + ＂ ＂ + self.make + ＂ ＂ + self.model         return long_name     def read_odometer(self):         print(＂this car has ＂ + str(self.odometer_reading) + ＂ miles on it＂)     def update_odometer(self, mileage):         if mileage >= self.odometer_reading:             self.odometer_reading = mileage         else:             print(＂you can not roll back an odometer＂)     def increment_odometer(self, miles):         self.odometer_reading += miles 2016 audi a4 this car has 23 miles on it ==================================== ###2.在一个模块中存储多个类 #新建一个Car()类，存储在car.py的模块中 class Car():          def __init__(self, make, model, year):         #一次模拟汽车的简单尝试         self.make = make         self.model = model         self.year = year         self.odometer_reading = 0     def get_descriptive_name(self):         long_name = str(self.year) + ＂ ＂ + self.make + ＂ ＂ + self.model         return long_name     def read_odometer(self):         print(＂this car has ＂ + str(self.odometer_reading) + ＂ miles on it＂)     def update_odometer(self, mileage):         if mileage >= self.odometer_reading:             self.odometer_reading = mileage         else:             print(＂you can not roll back an odometer＂)     def increment_odometer(self, miles):         self.odometer_reading += miles          class Battery():#定义一个名为Battery的新类     #模拟电动车的简单尝试     def __init__(self, battery_size = 70):     #初始化电瓶属性         self.battery_size = battery_size          def describe_battery(self):#给子类定义方法         #打印一条描述电池容量的消息         print(＂this car has ＂ + str(self.battery_size) + ＂-kwh battery＂)          class ElectricCar(Car):#创建一个子类，继承父类     #电动车的独特之处          def __init__(self, make, model, year):#接受父类的信息         #初始化父类的属性,super()函数帮助关联父类和子类         super(). __init__(make, model, year)         self.battery = Battery()#添加一个名为self.battery的属性，并将Battery()实例存储在属性self.battery中 2016 tesla model s this car has 70-kwh battery ========================================== ###3.从一个模块中导入多个类 from car import Car, ElectricCar  my_beetle = Car(＂bmw＂, ＂q7＂, 2016) print(my_beetle.get_descriptive_name())  my_tesla = ElectricCar(＂tesla＂, ＂model s＂, 2016) print(my_tesla.get_descriptive_name()) 2016 bmw q7 2016 tesla model s ============================================= ###4.导入整个模块 import car  my_beetle = Car(＂bmw＂, ＂q7＂, 2016) print(my_beetle.get_descriptive_name())  my_tesla = ElectricCar(＂tesla＂, ＂model s＂, 2016) print(my_tesla.get_descriptive_name()) 2016 bmw q7 2016 tesla model s ============================================ ###5.导入模块中的所有类 from module_name import * ====================================== ###6.在一个模块中导入另一个模块 #将Car类存储在car.py文件中，将 ElectricCar和Battery存储在一个叫electric_car.py的文件中 #如何创建car.py文件 class Car():     --snip--     #如何创建electric_car.py文件 from car import Car#将Car类导入到该模块中，因为ElectricCar类需要访问其父类Car class Battery():     --snip--      class ElectricCar(Car)；     --snip-- #新建一个my_cars.py的文件 from car import Car from electric_car import ElectricCar  my_beetle = Car(＂bmw＂, ＂q7＂, 2016) print(my_beetle.get_descriptive_name())  my_tesla = ElectricCar(＂tesla＂, ＂model s＂, 2016) print(my_tesla.get_descriptive_name()) 2016 bmw q7 2016 tesla model s