#3 Python面向对象（二）

1 class Doctor:
2     ‘‘‘
3     类变量的初始化
4     ‘‘‘
5     salary = 100  # salary为类变量
6 
7     def talk():
8         print(‘I am a doctor‘)

class Doctor:
    ‘‘‘
    在类中函数体外访问类变量salary
    ‘‘‘
    salary = 100
    print(salary)

    def talk(self):
        print(‘I am a doctor‘)


lisi = Doctor()   # 一旦实例化后，就会自动按顺序执行类中函数体外的代码


# 运行结果：
100

class Doctor:
    ‘‘‘
    在类中函数体内访问类变量salary
    ‘‘‘
    salary = 100

    def talk0(self):
        ‘‘‘
        使用类.类变量访问
        ‘‘‘
        print(‘My salary is {0}‘.format(Doctor.salary))

    def talk1(self):
        ‘‘‘
        使用实例.类变量访问
        ‘‘‘
        print(‘My salary is {0}‘.format(self.salary))


lisi = Doctor()

lisi.talk0()
lisi.talk1()


# 运行结果：
My salary is 100
My salary is 100

class Doctor:
    ‘‘‘
    在类外访问类变量salary
    ‘‘‘
    salary = 100

    def talk(self):
        print(‘I am a doctor‘)


lisi = Doctor()
print(Doctor.salary)  # 使用 类.类变量 访问
print(lisi.salary)   # 使用 实例.类变量 访问


# 运行结果：
100
100

1 class Doctor:
2     ‘‘‘
3     初始化实例变量
4     ‘‘‘
5 
6     def talk(self):
7         self.sentence = ‘I am man‘    # self.sentence 为实例变量

class Doctor:
    ‘‘‘
    类中函数体内的访问
    ‘‘‘

    def talk(self):
        self.sentence = ‘I am man‘    # 初始化实例变量self.sentence
        print(self.sentence)   # 访问实例变量


lisi = Doctor()

lisi.talk()  # 调用talk方法


# 运行结果：
I am man

class Doctor:
    ‘‘‘
    类外访问实例变量
    ‘‘‘

    def talk(self):
        self.sentence = ‘I am man‘    # 初始化实例变量self.sentence


lisi = Doctor()

lisi.talk()  # 必须先执行talk方法才能访问talk方法里面的实例变量
print(lisi.sentence)  # 类外访问实例变量

class Doctor:
    salary = 100

    def talk(self):
    ¦   print(‘I am a doctor‘)


print(salary)

# salary是Doctor的类变量，在类中定义
# 但在主程序中并不能被正确访问
# 因为salary变量是局部变量


# 运行结果：
Traceback (most recent call last):
  File "8.py", line 8, in <module>
    print(salary)
NameError: name ‘salary‘ is not defined

# 抛出变量未定义异常

class Doctor:
    def talk(self):
        self.salary = 100


print(salary)

# 同样，实例变量self.salary也是局部变量


# 运行结果：
Traceback (most recent call last):
  File "9.py", line 6, in <module>
    print(salary)
NameError: name ‘salary‘ is not defined

# 抛出变量未定义异常

class Doctor:
    def talk(self):
        self.salary = 100


Doctor().talk()
print(salary)

# 即使执行了talk方法，也不能正确访问
# 因为它至始至终都是局部变量

# 运行结果：
Traceback (most recent call last):
  File "9.py", line 12, in <module>
    print(salary)
NameError: name ‘salary‘ is not defined

class Doctor:
    salary = 100
    print(salary)

    def talk(self):
        print(Doctor.salary)

    def eat(self):
        print(Doctor.salary)


lisi = Doctor()
lisi.talk()
lisi.eat()

# 因为类变量在整个类中都是共有的
# 因此类变量能被类中的方法访问
# 换句话说，在类中类变量相当于全局变量

# 运行结果：

  100
  100
  100

class Doctor:
    salary = 100
    print(salary)

    def talk(self):
        self.food = ‘BaoZi‘
        print(Doctor.salary)
        print(self.food)

    def eat(self):
        print(Doctor.salary)
        print(self.food)


lisi = Doctor()
lisi.talk()
lisi.eat()

# 在talk方法里面定义实例变量self.food
# 但是在eat方法里面却可以访问self.food这个实例变量
#（前提是必须先运行talk方法，就相当于初始化self.food）
# 因此，在实例中，类变量和实例变量都相当于全局变量


# 运行结果：

  100
  100
  BaoZi
  100
  BaoZi

class Doctor:

    def talk(self):
        salary = 100
        print(salary)

    def eat(self):
        print(salary)


lisi = Doctor()
lisi.talk()
lisi.eat()

# 在类中talk方法里定义局部变量salary
# 在其他方法中是不能被访问的


# 运行结果：
100
Traceback (most recent call last):
  File "12.py", line 13, in <module>
    lisi.eat()
  File "12.py", line 8, in eat
    print(salary)
NameError: name ‘salary‘ is not defined

class Doctor:
    salary = 100  # 初始化类变量salary

    def talk0(self):
        print(‘talk0:‘, Doctor.salary)
        Doctor.salary = 200   # 修改类变量salary的值为200

    def talk1(self):
        print(‘talk1:‘, Doctor.salary)
        print(‘talk1:‘, self.salary)
        self.salary = 300   # 修改self.salary的值为300

    def talk2(self):
        print(‘talk2:‘, self.salary)
        print(‘talk2:‘, Doctor.salary)  # 输出的类变量并没有被改变为300


lisi = Doctor()

lisi.talk0()
lisi.talk1()
lisi.talk2()


# 运行结果：
talk0: 100
talk1: 200
talk1: 200
talk2: 300
talk2: 200