第九章?类
1.创建和实用类
①.创建Dog类
class Dog():
#__init__()是一种特殊的方法，每当根据Dog类创建新实例时，Python都会自动运行它
#开头和结尾带有__是一种约束，旨在避免Python默认方法与普通方法发生冲突
def __init__(self,name,age):
"""初始化属性name和age"""
self.name = name
self.age = age
def sit(self):
"""模拟小狗蹲下"""
print(self.name.title() + " is now sitting! ")
def roll_over(self):
"""模拟小狗打滚"""
print(self.name.title()+" is rolling!")
#根据类创建实例
my_dog = Dog('tom',6)
# 访问属性
print("My dog is "+my_dog.name.title())
print("My dog is "+str(my_dog.age)+" years old!")
# 调用方法
my_dog.sit()
my_dog.roll_over()
运行结果如下：
?2.使用类和实例
①.Car类
# class Car():
# def __init__(self,make,model,year):
# """初始化描述汽车的属性"""
# self.make = make
# self.model = model
# self.year = year
#
# def get_descriptive_name(self):
# long_name = str(self.year)+' '+self.make+' '+self.model
# return long_name.title()
#
# my_new_car = Car('audi','a4',2016)
# print(my_new_car.get_descriptive_name())
运行结果：
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②.给属性指定默认值
# class Car():
# def __init__(self,make,model,year):
# """初始化描述汽车的属性"""
# self.make = make
# self.model = model
# self.year = str(year)
# self.odometer_reading = 0
#
# def get_descriptive_name(self):
# long_name = self.year + " " + self.make + " " + self.model
# return long_name.title()
#
# def read_odometer(self):
# """打印一条指出汽车里程的消息"""
# print("This car has "+ str(self.odometer_reading)+" miles on it")
#
# my_new_car = Car('audi','a4',2016)
# print(my_new_car.get_descriptive_name())
# my_new_car.read_odometer()
运行结果：
?③.修改属性的值
#方法1.直接修改属性的值
# class Car():
# def __init__(self,make,model,year):
# """初始化描述汽车的属性"""
# self.make = make
# self.model = model
# self.year = str(year)
# self.odometer_reading = 0
#
# def get_descriptive_name(self):
# long_name = self.year + " " + self.make + " " + self.model
# return long_name.title()
# def read_odometer(self):
# """打印一条指出汽车里程的消息"""
# print("This car has "+ str(self.odometer_reading)+" miles on it")
#
# my_new_car = Car('audi','a4',2016)
# print(my_new_car.get_descriptive_name())
# my_new_car.odometer_reading = 23
# my_new_car.read_odometer()
运行结果：
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#方法2.通过方法修改属性的值
# class Car():
# def __init__(self,make,model,year):
# """初始化描述汽车的属性"""
# self.make = make
# self.model = model
# self.year = str(year)
# self.odometer_reading = 0
#
# def get_descriptive_name(self):
# long_name = self.year + " " + self.make + " " + self.model
# return long_name.title()
#
# def read_odometer(self):
# """打印一条指出汽车里程的消息"""
# print("This car has "+ str(self.odometer_reading)+" miles on it")
#
# def update_odometer(self,mileage):
# """将里程表读数设置为指定的值"""
# self.odometer_reading = mileage
#
# my_new_car = Car('audi','a4',2016)
# print(my_new_car.get_descriptive_name())
#
# my_new_car.update_odometer(23)
# my_new_car.read_odometer()
运行结果：
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#方法3.通过方法对属性的值进行递增
class Car():
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
self.make = make
self.model = model
self.year = str(year)
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = self.year + " " + self.make + " " + self.model
return long_name.title()
def read_odometer(self):
"""打印一条指出汽车里程的消息"""
print("This car has "+ str(self.odometer_reading)+" miles on it")
def update_odometer(self, mileage):
"""将里程表读数设置为指定的值"""
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self,miles):
"""将里程表读数增加指定的量"""
self.odometer_reading += miles
my_new_car = Car('audi','a4',2016)
print(my_new_car.get_descriptive_name())
my_new_car.increment_odometer(12)
my_new_car.update_odometer(10)
my_new_car.read_odometer()
运行结果：
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3.继承
# 编写类时，并非总是要从空白开始。如果你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，他将自动获得另一个类的所有属性和方法 #原有的类成为父类，新类为子类 #出了继承父类的属性和方法，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
#创建子类时，父类必须包含在当前文件中，且位于子类前面
#定义子类时，必须在括号内指定父类的名称
# class Car():
# def __init__(self,make,model,year):
# """初始化描述汽车的属性"""
# 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):
# """打印一条指出汽车里程的消息"""
# 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't roll back an odometer!")
#
# def increment_odometer(self,miles):
# self.odometer_reading += miles
# class ElectricCar(Car): # """电动汽车的独特之处""" # def __init__(self,make,model,year): # """初始化父类的属性""" # super().__init__(make,model,year) # #super()帮助python将父类和子类关联起来
# 创建ElectricCar实例，赋给变量my_tesla
# my_tesla = ElectricCar('tesla','models',2016)
# print(my_tesla.get_descriptive_name())
运行结果：
?2.给子类定义属性和方法
# class ElectricCar(Car):
# """电动汽车的独特之处"""
# def __init__(self,make,model,year):
# """初始化父类的属性，再初始化电动汽车特有的属性"""
# super().__init__(make,model,year)
# self.battery_size = 70
#
# def describe_battery(self):
# """打印一条描述电瓶容量的消息"""
# print("This car has a "+str(self.battery_size)+"-kwh battery.")
#
# my_tesla = ElectricCar('tesla','models',2016)
# print(my_tesla.get_descriptive_name())
# my_tesla.describe_battery()
运行结果：
?3.重写父类的方法和将实例用作属性
#对于父类的方法，只要他不符合子类模拟的实物的行为，都可以对其进行重写
#重写完后，调用时会自动忽略父类的方法，只运行子类的方法
#当类的属性过多，可以提出来一部分单独列出来
class Car():
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
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):
"""打印一条指出汽车里程的消息"""
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't roll back an odometer!")
def increment_odometer(self,miles):
self.odometer_reading += miles
class Battery():
"""一次模拟电动汽车电瓶的简单尝试"""
def __init__(self,battery_size=70):
"""初始化电瓶的属性"""
self.battery_size = battery_size
def describe_battery(self):
"""打印一条描述电瓶容量的消息"""
print("This car has a "+str(self.battery_size)+"-kwh battery.")
def get_range(self):
"""打印一条消息，指出电瓶的续航里程"""
if self.battery_size == 70:
range = 240
elif self.battery_size == 85:
range = 270
else:
range = 60
message = "This car can go approximately "+str(range)
message += " miles on a full charge."
print(message)
class ElectricCar(Car):
"""电动汽车的独特之处"""
def __init__(self,make,model,year):
"""初始化父类的属性，再初始化电动汽车特有的属性"""
super().__init__(make,model,year)
self.battery = Battery()
my_tesla = ElectricCar('tesla','models',2016)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()
运行结果：
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4.导入类
car.py
"""一个可用于表示汽车的类"""
class Car():
def __init__(self,make,model,year):
"""初始化描述汽车的属性"""
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):
"""打印一条指出汽车里程的消息"""
print("This car has "+ str(self.odometer_reading)+" miles on it")
def update_odometer(self,mileage):
"""将里程表读数设置为指定的值，拒绝将里程表往回拨"""
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self,miles):
"""将里程表读数增加指定的量"""
self.odometer_reading += miles
class Battery():
"""一次模拟电动汽车电瓶的简单尝试"""
def __init__(self,battery_size=70):
"""初始化电瓶的属性"""
self.battery_size = battery_size
def describe_battery(self):
"""打印一条描述电瓶容量的消息"""
print("This car has a "+str(self.battery_size)+"-bwh battery.")
def get_range(self):
"""打印一条描述电瓶续航里程的消息"""
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)
class ElertricCar(Car):
"""模拟电动车的独特之处"""
def __init__(self,make,model,year):
"""初始化父类的属性，再初始化电动汽车特有的属性"""
super().__init__(make,model,year)
self.battery = Battery()
my_car.py
from car import Car
my_new_car = Car('audi','a4',2016)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
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