【python进阶】python中的类、继承、多态

梦里梦外; 2022-03-26 04:40 198阅读 0赞

定义一个python类：

class Point:
        def __init__(self, x = 0, y = 0):
            self.x, self.y = x, y
    p = Point(10, 10)
    print(type(p))
    print(p.x, p.y)
    print(dir(Point))
    print(help(Point))

输出：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zNjM3Mjg3OQ_size_16_color_FFFFFF_t_70]  
dir可以打印这个类里面的所有方法。  
help可以查看帮助信息

--------------------

### 类的构造 ###

Python 没有 public / protected / private这样的访问控制，如果你非要表示“私有”，习惯是加双下划线前缀。

class Point:
        def __init__(self, x=0, y=0):
            self.__x, self.__y = x, y
    
        def set(self, x, y):
            self.__x, self.__y = x, y
    
        def __f(self):
            pass

p = Point(10, 10)
    print(p.__x)

![在这里插入图片描述][20190114205722311.png]

--------------------

### 类的继承 ###

class Person(object):
        def __init__(self,name,sex):
            self.name = name
            self.sex = sex
            
        def print_title(self):
            if self.sex == "male":
                print("man")
            elif self.sex == "female":
                print("woman")
    
    class Child(Person):                            # Child 继承 Person
        pass
                
    May = Child("May","female")
    Peter = Person("Peter","male")
    
    print(May.name,May.sex,Peter.name,Peter.sex)    # 子类继承父类方法及属性
    May.print_title()
    Peter.print_title()

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zNjM3Mjg3OQ_size_16_color_FFFFFF_t_70 1]  
可以看到child是继承person的。  
Python 有两个判断继承的函数：isinstance() 用于检查实例类型；issubclass() 用于检查类继承。参见下方示例：

class Person(object):
        pass
    
    class Child(Person):                 # Child 继承 Person
        pass
    
    May = Child()
    Peter = Person()    
    
    print(isinstance(May,Child))         # True
    print(isinstance(May,Person))        # True
    print(isinstance(Peter,Child))       # False
    print(isinstance(Peter,Person))      # True
    print(issubclass(Child,Person))      # True

--------------------

### python类的多态 ###

这里重写了print\_title函数

class Person(object):
        def __init__(self,name,sex):
            self.name = name
            self.sex = sex
            
        def print_title(self):
            if self.sex == "male":
                print("man")
            elif self.sex == "female":
                print("woman")
    
    class Child(Person):                # Child 继承 Person
        def print_title(self):
            if self.sex == "male":
                print("boy")
            elif self.sex == "female":
                print("girl")
            
    May = Child("May","female")
    Peter = Person("Peter","male")
    
    print(May.name,May.sex,Peter.name,Peter.sex)
    May.print_title()
    Peter.print_title()

![在这里插入图片描述][20190115164721764.png]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zNjM3Mjg3OQ_size_16_color_FFFFFF_t_70]: /images/20220326/fede5e5092884235bfe381c9cdc16f64.png
[20190114205722311.png]: /images/20220326/362228a3d60c4fc89f8b072c796dc139.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zNjM3Mjg3OQ_size_16_color_FFFFFF_t_70 1]: /images/20220326/b2e5b8ce9bf74c0a8bfebb3136ca03bf.png
[20190115164721764.png]: /images/20220326/12f8293e868541bf83be351a4974180d.png