python基礎(13)-面向對象

類

類的定義和使用

 1 #
 2 class Person:
 3     def __init__(self, name, age, gender):
 4         self.name = name
 5         self.age = age
 6         self.gender = gender
 7 
 8     def show(self):
 9         print(self.name)
10 
11 
12 # 實例化
13 person1 = Person('張三', 18, '男')
14 person2 = Person('李四', 20, '女')
15 person1.show()  # 張三
16 person2.show()  # 李四

類方法和靜態方法

 1 class A:
 2     @classmethod
 3     def print1(self):
 4         print('print in class method')
 5 
 6     @staticmethod
 7     def print2():
 8         print('print in static method')
 9 
10 A.print1()  # print in class method
11 A.print2()  # print in static method

接口和抽象類

因爲python 沒有抽象類、接口的概念，因此要實現這種功能得abc.py 這個類庫,具體方式以下

接口

全部方法都必須在子類中實現

 1 import abc
 2 
 3 class AInterface(metaclass=abc.ABCMeta):
 4     @abc.abstractmethod
 5     def func1(self): pass
 6 
 7 class A(AInterface):
 8     def func1(self): pass
 9 
10 a = A()  
11 # 不實現則報錯
12 # TypeError: Can't instantiate abstract class A with abstract methods func1

抽象類

部分方法在子類中實現

 1 import abc
 2 
 3 class AInterface(metaclass=abc.ABCMeta):
 4     @abc.abstractmethod
 5     def func1(self): pass
 6 
 7     def func2(self): pass
 8 
 9 class A(AInterface):
10     def func1(self): pass
11 
12 a = A()
13 a.func2()
14 # 不實現則報錯
15 # TypeError: Can't instantiate abstract class A with abstract methods func1

三大特性

繼承

• 單繼承

   1 class A:
   2     def print(self):
   3         print("print from A")
   4 
   5 # B繼承A
   6 class B(A): pass
   7 
   8 # C繼承A
   9 class C(A):
  10     def print(self):
  11         print('print from C')
  12 
  13 b = B()
  14 b.print()  # print from A
  15 c = C()
  16 c.print()  # print from C

  當調用的方法在父類中已經存在同名方法,會默認調用子類的方法.如C類.若是子類中沒有,則會調用父類的方法,如B類.

• 多繼承

   1 class A:
   2     def print(self):
   3         print('print from A')
   4 
   5 
   6 class B:
   7     def print(self):
   8         print('print from B')
   9 
  10 
  11 class C1(A, B): pass
  12 
  13 
  14 class C2(B, A): pass
  15 
  16 
  17 # C1類繼承A類B類 C2類繼承B類和A類
  18 c1 = C1()
  19 c1.print()  # print from A
  20 c2 = C2()
  21 c2.print()  # print from B

  一個類繼承多個類時,當調用的方法子類中沒有時,會按繼承順序(從左到右)依次在父類中尋找並調用

• 派生

  子類擁有父類沒有的方法或屬性

   1 class A:
   2     def print(self):
   3         print('print from A')
   4 
   5 
   6 class B(A):
   7     def myprint(self):
   8         print('print from B')
   9 
  10 
  11 b = B()
  12 b.print()  # print from A
  13 b.myprint()  # print from B

• 鑽石繼承(super()的執行順序)

   1 class A:
   2     def print(self):
   3         print("print from A")  # print from A  5
   4 
   5 class B(A):
   6     def print(self):
   7         print('print from B')  # print from B  1
   8         print(super().print)  # <bound method C.print of <__main__.D object at 0x00000000021EC6D8>>  2
   9         super().print()
  10 
  11 class C(A):
  12     def print(self):
  13         print('print from C')  # print from C  3
  14         print(super().print)  # <bound method A.print of <__main__.D object at 0x00000000021EC6D8>>  4
  15         super().print()
  16 
  17 class D(B, C):
  18     pass
  19 
  20 d = D()
  21 d.print()
  22 
  23 # result:
  24 # print from B
  25 # <bound method C.print of <__main__.D object at 0x00000000021EC6D8>>
  26 # print from C
  27 # <bound method A.print of <__main__.D object at 0x00000000021EC6D8>>
  28 # print from A

多態

python原生支持多態

• java中的多態

   1 public interface Animal {
   2     void talk();
   3 }
   4 
   5 public class Dog implements Animal{
   6     @Override
   7     public void talk() {
   8         System.out.println("wangwang");
   9     }
  10 }
  11 
  12 public class Pig implements Animal {
  13     @Override
  14     public void talk() {
  15         System.out.println("aoao");
  16     }
  17 }
  18 
  19 public class Main {
  20     public static void main(String[] args) {
  21         Animal dog = new Dog();
  22         dog.talk();
  23         Animal pig = new Pig();
  24         pig.talk();
  25     }
  26 }

• python中的多態

   1 import abc
   2 
   3 class Animal(metaclass=abc.ABCMeta):
   4     @abc.abstractmethod
   5     def talk(self): pass
   6 
   7 class Pig(Animal):
   8     def talk(self):
   9         print('aoao')
  10 
  11 class Dog(Animal):
  12     def talk(self):
  13         print('wangwang')
  14 
  15 dog = Dog()
  16 dog.talk()
  17 pig = Pig()
  18 pig.talk()

封裝

• 私有屬性

  屬性\方法名前加雙下劃線聲明私有屬性\方法.對應java中private,默認public,無protect.(*在類的外部仍然能夠經過實例._類名__屬性名調用)

   1 class Person:
   2     def __init__(self, name, age, gender, pwd):
   3         self.name = name
   4         self.__age = age
   5         self.gender = gender
   6         self.pwd = pwd
   7 
   8     def __getpwd(self):
   9         return self.pwd
  10 
  11 
  12 person = Person('張三', 18, '男', '123')
  13 print(person.name)
  14 # print(person.__age)  # AttributeError: 'Person' object has no attribute '__age'
  15 print(person._Person__age)  # 18
  16 print(person.__getpwd())  # AttributeError: 'Person' object has no attribute '__getpwd'

• 封裝屬性

  @property能夠將方法封裝成屬性

   1 class Person:
   2     def __init__(self, name, age):
   3         self.__name = name
   4         self.__age = age
   5 
   6     @property
   7     def name(self):
   8         return self.__name
   9 
  10     @name.setter
  11     def name(self, new_name):
  12         self.__name = new_name
  13 
  14     @name.deleter
  15     def name(self):
  16         print('執行刪除name操做')
  17 
  18 
  19 p = Person('張三', 18)
  20 print(p.name)  # 張三
  21 p.name = '李四'
  22 print(p.name)  # 李四
  23 # 只是觸發對應deleter裝飾的函數,具體操做需在函數類完成
  24 del p.name  # 執行刪除name操做
  25 print(p.name)  # 李四