python基础(13)-面向对象

类

类的定义和使用

 #
 class Person:
     def __init__(self, name, age, gender):
         self.name = name
         self.age = age
         self.gender = gender

     def show(self):
         print(self.name)

 # 实例化
 person1 = Person('张三', 18, '男')
 person2 = Person('李四', 20, '女')
 person1.show()  # 张三
 person2.show()  # 李四

类方法和静态方法

 class A:
     @classmethod
     def print1(self):
         print('print in class method')

     @staticmethod
     def print2():
         print('print in static method')

 A.print1()  # print in class method
 A.print2()  # print in static method

接口和抽象类

由于python 没有抽象类、接口的概念，所以要实现这种功能得abc.py 这个类库,具体方式如下

接口

所有方法都必须在子类中实现

 import abc

 class AInterface(metaclass=abc.ABCMeta):
     @abc.abstractmethod
     def func1(self): pass

 class A(AInterface):
     def func1(self): pass

 a = A()
 # 不实现则报错
 # TypeError: Can't instantiate abstract class A with abstract methods func1

抽象类

部分方法在子类中实现

 import abc

 class AInterface(metaclass=abc.ABCMeta):
     @abc.abstractmethod
     def func1(self): pass

     def func2(self): pass

 class A(AInterface):
     def func1(self): pass

 a = A()
 a.func2()
 # 不实现则报错
 # TypeError: Can't instantiate abstract class A with abstract methods func1

三大特性

继承

• 单继承

   class A:
       def print(self):
           print("print from A")
  
   # B继承A
   class B(A): pass
  
   # C继承A
   class C(A):
       def print(self):
           print('print from C')
  
   b = B()
   b.print()  # print from A
   c = C()
   c.print()  # print from C

  当调用的方法在父类中已经存在同名方法,会默认调用子类的方法.如C类.如果子类中没有,则会调用父类的方法,如B类.

• 多继承

   class A:
       def print(self):
           print('print from A')
  
   class B:
       def print(self):
           print('print from B')
  
   class C1(A, B): pass
  
   class C2(B, A): pass
  
   # C1类继承A类B类 C2类继承B类和A类
   c1 = C1()
   c1.print()  # print from A
   c2 = C2()
   c2.print()  # print from B

  一个类继承多个类时,当调用的方法子类中没有时,会按继承顺序(从左到右)依次在父类中寻找并调用

• 派生

  子类拥有父类没有的方法或属性

   class A:
       def print(self):
           print('print from A')
  
   class B(A):
       def myprint(self):
           print('print from B')
  
   b = B()
   b.print()  # print from A
   b.myprint()  # print from B

• 钻石继承(super()的执行顺序)

   class A:
       def print(self):
           print("print from A")  # print from A  5
  
   class B(A):
       def print(self):
           print('print from B')  # print from B  1
           print(super().print)  # <bound method C.print of <__main__.D object at 0x00000000021EC6D8>>  2
           super().print()
  
   class C(A):
       def print(self):
           print('print from C')  # print from C  3
           print(super().print)  # <bound method A.print of <__main__.D object at 0x00000000021EC6D8>>  4
           super().print()
  
   class D(B, C):
       pass
  
   d = D()
   d.print()
  
   # result:
   # print from B
   # <bound method C.print of <__main__.D object at 0x00000000021EC6D8>>
   # print from C
   # <bound method A.print of <__main__.D object at 0x00000000021EC6D8>>
   # print from A

  

多态

python原生支持多态

• java中的多态

   public interface Animal {
       void talk();
   }
  
   public class Dog implements Animal{
       @Override
       public void talk() {
           System.out.println("wangwang");
       }
   }
  
   public class Pig implements Animal {
       @Override
       public void talk() {
           System.out.println("aoao");
       }
   }
  
   public class Main {
       public static void main(String[] args) {
           Animal dog = new Dog();
           dog.talk();
           Animal pig = new Pig();
           pig.talk();
       }
   }

• python中的多态

   import abc
  
   class Animal(metaclass=abc.ABCMeta):
       @abc.abstractmethod
       def talk(self): pass
  
   class Pig(Animal):
       def talk(self):
           print('aoao')
  
   class Dog(Animal):
       def talk(self):
           print('wangwang')
  
   dog = Dog()
   dog.talk()
   pig = Pig()
   pig.talk()

封装

• 私有属性

  属性\方法名前加双下划线声明私有属性\方法.对应java中private,默认public,无protect.(*在类的外部仍然可以通过实例._类名__属性名调用)

   class Person:
       def __init__(self, name, age, gender, pwd):
           self.name = name
           self.__age = age
           self.gender = gender
           self.pwd = pwd
  
       def __getpwd(self):
           return self.pwd
  
   person = Person(')
   print(person.name)
   # print(person.__age)  # AttributeError: 'Person' object has no attribute '__age'
  
   print(person.__getpwd())  # AttributeError: 'Person' object has no attribute '__getpwd'

• 封装属性

  @property可以将方法封装成属性

   class Person:
       def __init__(self, name, age):
           self.__name = name
           self.__age = age
  
       @property
       def name(self):
           return self.__name
  
       @name.setter
       def name(self, new_name):
           self.__name = new_name
  
       @name.deleter
       def name(self):
           print('执行删除name操作')
  
   p = Person('张三', 18)
   print(p.name)  # 张三
   p.name = '李四'
   print(p.name)  # 李四
   # 只是触发对应deleter装饰的函数,具体操作需在函数类完成
   del p.name  # 执行删除name操作
   print(p.name)  # 李四