python 类 - 继承
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继承
什么是继承?
- 编写类时,并非总要从空白开始。如果要编写的类是另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。现有的类称为父类,而新类称为子类。
- 子类继承了其父类的所有属性和方法,同时也可以定义自己的属性和方法。
1、子类的方法__init__
创建子类时,首先要完成的是将父类的所有属性和方法继承,这里使用子类的方法 __init__();
#继承
#子类的方法__init__()
class Car():
"""一次模拟汽车的简单尝试"""
def __init__(self,make,model,year):
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.title()
def read_odometer(self):
print("This car has" + str(self.odometer_reading) + "mile on it.")
def update_odomter(self,mileage):
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self,miles):
self.odometer_reading += miles
class ElectricCar(Car):
"""电动汽车的独特"""
def __init__(self,make,model,year):
"""初始化父类的属性"""
super().__init__(make,model,year)
my_tesla = ElectricCar('tesla','model X',2018)
print(my_tesla.get_descriptive_name())
执行结果:
1 2018 Tesla Model X
注意点:
- 创建子类时,父类必须包含在当前文件中,且位于子类前面。
- super()是一个特殊函数,帮助父类和子类关联起来。
- 父类也称为超类(superclass)
1.1、给子类定义属性和方法
在一个类继承另一类后,可添加区分子类和父类所需的新属性和方法。
1 class Car(): 2 """一次模拟汽车的简单尝试""" 3 def __init__(self,make,model,year): 4 self.make = make 5 self.model = model 6 self.year = year 7 self.odometer_reading = 0 8 9 def get_descriptive_name(self): 10 long_name = str(self.year) + " " + self.make + " " + self.model 11 return long_name.title() 12 13 def read_odometer(self): 14 print("This car has" + str(self.odometer_reading) + "mile on it.") 15 16 def update_odomter(self,mileage): 17 if mileage >= self.odometer_reading: 18 self.odometer_reading = mileage 19 20 else: 21 print("You can't roll back an odometer!") 22 23 def increment_odometer(self,miles): 24 self.odometer_reading += miles 25 26 class ElectricCar(Car): 27 """电动汽车的独特""" 28 29 def __init__(self,make,model,year): 30 """初始化父类的属性""" 31 super().__init__(make,model,year) 32 33 # 给子类定义属性和方法 34 self.battery_size = 70 35 36 #给子类定义属性和方法 37 def describe_battery(self): 38 """打印一条描述电瓶容量的消息""" 39 print("This car has a " + str(self.battery_size) + "-KWh battery.") 40 41 my_tesla = ElectricCar('tesla','model X',2018) 42 print(my_tesla.get_descriptive_name()) 43 my_tesla.describe_battery()View Code
执行结果:
1 2018 Tesla Model X 2 This car has a 70-KWh battery.
1.2、重写父类的方法
- 如果父类中存在的一个方法完全不适用于子类,那么可以直接在子类中对父类的方法进行重写。
- 要求子类中重写的方法要与父类的同名,这样代码就不会执行父类方法,而只关注子类的方法
1 class Car(): 2 --snip-- 3 4 def fill_gas_tank(): 5 """油箱""" 6 print("This car need a gas tank.") 7 8 class ElectricCar(Car): 9 --snip-- 10 #重写父类的方法 11 def fill_gas_tank(): 12 """电动汽车没有油箱""" 13 print("This car doesn't need a gas tank.")
1.3、将实例用作属性
- 定义一个新类,并且没有任何继承
- 在子类中,添加一个属性,指向新建的父类;这里是self.battery = Battery()
1 class Car(): 2 """一次模拟汽车的简单尝试""" 3 def __init__(self,make,model,year): 4 self.make = make 5 self.model = model 6 self.year = year 7 self.odometer_reading = 0 8 9 def get_descriptive_name(self): 10 long_name = str(self.year) + " " + self.make + " " + self.model 11 return long_name.title() 12 13 def read_odometer(self): 14 print("This car has" + str(self.odometer_reading) + "mile on it.") 15 16 def update_odomter(self,mileage): 17 if mileage >= self.odometer_reading: 18 self.odometer_reading = mileage 19 20 else: 21 print("You can't roll back an odometer!") 22 23 def increment_odometer(self,miles): 24 self.odometer_reading += miles 25 26 27 # 将实例用作属性 28 class Battery(): 29 def __init__(self, battery_size=70): 30 """初始化电瓶的属性""" 31 self.battery_size = battery_size 32 33 def describe_battery(self): 34 """打印一条描述电瓶容量的信息""" 35 print("This car has a" + str(self.battery_size) + "-KWh battery.") 36 37 38 class ElectricCar(Car): 39 """电动汽车的独特""" 40 41 def __init__(self,make,model,year): 42 """初始化父类的属性""" 43 super().__init__(make,model,year) 44 45 # 给子类定义属性和方法 46 # self.battery_size = 70 #新属性 47 #初始化父类的属性,再初始化电动车特有的属性 48 self.battery = Battery() 49 50 # #给子类定义属性和方法 51 # def describe_battery(self): 52 # """打印一条描述电瓶容量的消息""" 53 # print("This car has a " + str(self.battery_size) + "-KWh battery.") 54 55 #重写父类的方法 56 def fill_gas_tank(): 57 """电动汽车没有油箱""" 58 print("This car doesn't need a gas tank.") 59 60 61 my_tesla = ElectricCar('tesla','model X',2018) 62 print(my_tesla.get_descriptive_name()) 63 # my_tesla.describe_battery() 64 my_tesla.battery.describe_battery()
执行结果:
1 2018 Tesla Model X 2 This car has a70-KWh battery.
继续将实例用作属性
class Car(): --snip--# 将实例用作属性 class Battery(): --snip--
#实例2 #打印一条消息,指出电瓶的续航里程 def get_range(self): if self.battery_size == 70: range = 240 elif self.battery_size == 85: range = 70 msg = "This car can go approximately" + str(range) msg += "miles on a full charge." print(msg) class ElectricCar(Car): --snip-- tr my_tesla = ElectricCar('tesla','model X',2018) print(my_tesla.get_descriptive_name()) my_tesla.battery.describe_battery() my_tesla.battery.get_range()
执行结果:
1 2018 Tesla Model X 2 This car has a70-KWh battery. 3 This car can go approximately240miles on a full charge.
标签:__,battery,python,self,odometer,继承,model,def 来源: https://www.cnblogs.com/aszeno/p/10398375.html