类的继承

类的继承

class Person(object):   # 定义一个父类
 
    def talk(self):    # 父类中的方法
        print("person is talking....")  
 
 
class Chinese(Person):    # 定义一个子类， 继承Person类
 
    def walk(self):      # 在子类中定义其自身的方法
        print('is walking...')
 
c = Chinese()
c.talk()      # 调用继承的Person类的方法
c.walk()     # 调用本身的方法
 
# 输出
 
person is talking....
is walking...

构造函数的继承

如果我们要给实例 c 传参，我们就要使用到构造函数，那么构造函数该如何继承，同时子类中又如何定义自己的属性？

继承类的构造方法：

        1.经典类的写法： 父类名称.__init__(self,参数1，参数2，...)

        2. 新式类的写法：super(子类，self).__init__(参数1，参数2，....)

class Person(object):
 
    def __init__(self, name, age):
        self.name = name
        self.age = age
        self.weight = 'weight'
 
    def talk(self):
        print("person is talking....")
 
 
class Chinese(Person):
 
    def __init__(self, name, age, language):  # 先继承，在重构
        Person.__init__(self, name, age)  #继承父类的构造方法，也可以写成：super(Chinese,self).__init__(name,age)
        self.language = language    # 定义类的本身属性
 
    def walk(self):
        print('is walking...')
 
 
class American(Person):
    pass
 
c = Chinese('bigberg', 22, 'Chinese')

super()继承父类

如果要在子类中引用父类的方法，但是又需要添加一些子类所特有的内容，可通过类名.方法()和super()来调用父类的方法，再个性化子类的对应函数。

直接使用类名.方法()来调用时，还是需要传入self为第一个参数，而使用super()调用则python自动将self传入，因此使用super()比较简洁。

如下animal基类和cat子类，cat类的__init__( )构造函数比父类多一个leg参数，eat()函数比父类多一行输出，通过super()调用父类的函数，则不需要将重复的部分再写一遍。

使用super()调用父类函数的好处：

1.简化代码

2.如果父类名称修改，对其他调用父类函数的类来说也没有影响，而如果直接使用父类的名称来调用，父类名称修改会影响其他所有的类。

class animal:
    def __init__(self,name,sex,leg):
        self.name = name
        self.sex = sex
        self.leg = leg
    def eat(self,food):
        print('%s likes to eat %s'%(self.name,food))
class cat(animal):  #cat类继承animal类
    def __init__(self,name,sex,leg,tail):  #定义初始化构造函数，但是比父类多一个参数
        #animal.__init__(self,name,sex,leg)
        super().__init__(name,sex,leg)  #调用父类的初始化构造函数
        self.tail=tail
        print('cat has %s legs,and %s tail'%(self.leg,self.tail))
    def eat(self,food):  #定义eat函数，但是增加一行输出
        #animal.eat(self,food)
        super().eat(food)  #调用父类的方法
        print('%s also likes to eat %s' % (self.name, food))

cat1=cat('cat1','male',4,1)
cat1.eat('mouse')

# 输出如下：
# cat has 4 legs,and 1 tail
# cat1 likes to eat mouse
# cat1 also likes to eat mouse

 子类对父类方法的重写

class Person(object):
 
    def __init__(self, name, age):
        self.name = name
        self.age = age
        self.weight = 'weight'
 
    def talk(self):
        print("person is talking....")
 
class Chinese(Person):
 
    def __init__(self, name, age, language): 
        Person.__init__(self, name, age) 
        self.language = language
        print(self.name, self.age, self.weight, self.language)
 
    def talk(self):  # 子类 重构方法
        print('%s is speaking chinese' % self.name)
 
    def walk(self):
        print('is walking...')
 
c = Chinese('bigberg', 22, 'Chinese')
c.talk()
 
# 输出
bigberg 22 weight Chinese
bigberg is speaking chinese

事例：

class SchoolMember(object):
    '''学习成员基类'''
    member = 0
 
    def __init__(self, name, age, sex):
        self.name = name
        self.age = age
        self.sex = sex
        self.enroll()
 
    def enroll(self):
        '注册'
        print('just enrolled a new school member [%s].' % self.name)
        SchoolMember.member += 1
 
    def tell(self):
        print('----%s----' % self.name)
        for k, v in self.__dict__.items():
            print(k, v)
        print('----end-----')
 
    def __del__(self):
        print('开除了[%s]' % self.name)
        SchoolMember.member -= 1
 
 
class Teacher(SchoolMember):
    '教师'
    def __init__(self, name, age, sex, salary, course):
        SchoolMember.__init__(self, name, age, sex)
        self.salary = salary
        self.course = course
 
    def teaching(self):
        print('Teacher [%s] is teaching [%s]' % (self.name, self.course))
 
 
class Student(SchoolMember):
    '学生'
 
    def __init__(self, name, age, sex, course, tuition):
        SchoolMember.__init__(self, name, age, sex)
        self.course = course
        self.tuition = tuition
        self.amount = 0
 
    def pay_tuition(self, amount):
        print('student [%s] has just paied [%s]' % (self.name, amount))
        self.amount += amount
 
t1 = Teacher('Wusir', 28, 'M', 3000, 'python')
t1.tell()
s1 = Student('haitao', 38, 'M', 'python', 30000)
s1.tell()
s2 = Student('lichuang', 12, 'M', 'python', 11000)
print(SchoolMember.member)
del s2
 
print(SchoolMember.member)
 
 
 
# 输出
----end-----
just enrolled a new school member [haitao].
----haitao----
age 38
sex M
name haitao
amount 0
course python
tuition 30000
----end-----
just enrolled a new school member [lichuang].
3
开除了[lichuang]
2
开除了[Wusir]
开除了[haitao]