类内成员和方法的使用

class Dog():
    def __init__(self,name,age):
        self.name = name
        self.age = age
    def sit(self):
        print(self.name.title()+"is now setting")
    def rollOver(self):
        print(self.name + "is roll over")

#引用实例
myDog = Dog("小怪",4)
print("my dog is "+str(myDog.age)+" age!")   #my dog is 4 age!
myDog.sit()   #小怪is now setting
myDog.rollOver()  #小怪is roll over

其中的_init_(self)是必须的，相当于C++的构造函数，self是指向实例本身的引用，相当于C++类的this指针

#给属性指定默认值
class Car():
    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year
        self.odomete_reading = 0   #指定默认值
    def get_descriptive_name(self):
        long_name = str(self.year) + " " + self.model + " " + self.model
        return long_name.title()
    def read_odometer(self):
        print("the car has " + str(self.odomete_reading) + " mlies on it !")

#实例化一个car
my_new_car = Car('audi','a4',1998)
car_info = my_new_car.get_descriptive_name()
print(car_info)  #1998 A4 A4
my_new_car.read_odometer()  #the car has 0 mlies on it !

修改属性的值有三种方法：直接通过实例进行修改；通过方法进行设置；通过方法增加特定的值

#方法一

class Car():
    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year
        self.odomete_reading = 0
    def get_descriptive_name(self):
        long_name = str(self.year) + " " + self.make + " " +self.model
        return long_name
    def read_odometer(self):
        print("the car has " + str(self.odomete_reading) + " mlies!")
my_new_car = Car('audi','a4',1996)
my_new_car.odomete_reading = 10000
long_name = my_new_car.get_descriptive_name()
print(long_name)
my_new_car.read_odometer()  #直接在实例中修改属性的值

#方法二

class Car():
    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year
        self.odomete_reading = 0
    def get_descriptive_name(self):
        long_name = str(self.year) + " " + self.make + " " +self.model
        return long_name
    def read_odometer(self):
        print("the car has " + str(self.odomete_reading) + " mlies!")

    def update_odometer(self,mlies):
        self.odomete_reading = mlies
my_new_car = Car('audi','a4',1996)
my_new_car.update_odometer(9202)  #通过调用函数update_odometer来更新类内的属性
long_name = my_new_car.get_descriptive_name()
print(long_name)
my_new_car.read_odometer()  #the car has 9202 mlies!

#方法三

class Car():
    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year
        self.odomete_reading = 0
    def get_descriptive_name(self):
        long_name = str(self.year) + " " + self.make + " " +self.model
        return long_name
    def read_odometer(self):
        print("the car has " + str(self.odomete_reading) + " mlies!")

    def update_odometer(self,mlies):    #修改参数odomete_reading的值
        self.odomete_reading = mlies
    def increment_odometer(self,mlies):  #通过内部的方法来使的内部数据增加
        self.odomete_reading += mlies
my_new_car = Car('audi','a4',1996)
my_new_car.update_odometer(9202)  #通过调用函数update_odometer来更新类内的属性
my_new_car.read_odometer()  #the car has 9202 mlies!

long_name = my_new_car.get_descriptive_name()
print(long_name)

my_new_car.increment_odometer(20)
my_new_car.read_odometer()  #the car has 9222 mlies!