面向对象之封装、继承

一、面向对象

1、创建一个类的基本格式,并调用

1 class 类名：
2      def  __init__(self):  # 必写
3          "数据的封装"
4      def 方法名（self）:
5          "方法体"
6 
7 #   调用
8 对象名=类名（参数1，参数2....）
9 对象名.方法名（）

2、构造函数
类里的__init__方法属于构造函数，其作用是进行数据初始化

应用：

　　(1)将数据分装到对象中，供自己方法调用

 class FileHandler:
     def __init__(self,file_path):
         self.file_path = file_path
         self.f = open(self.file_path, 'rb')
 
      def read_first(self):
            # self.f.read()
          # ...
         pass
 
     def read_last(self):
         # self.f.read()
         # ...
         pass

     def read_second(self):
         # self.f...
         # ...
         pass
                             
 obj = FileHandler('C:/xx/xx.log')
 obj.read_first()
 obj.read_last()
 obj.read_second()
 obj.f.close()

　　(2)、将数据封装到对象中,以供其他函数调用

 1 def new_func(arg):
 2     arg.k1
 3     arg.k2
 4     arg.k6
 5 
 6 class Foo:
 7     def __init__(self,k1,k2,k6):
 8         self.k1 = k1
 9         self.k2 = k2
10         self.k6 = k6
11 
12 obj = Foo(111,22,333)
13 new_func(obj)

3、面向对象代码的编写
方式一：归类+提取公共值

 1 class File:
 2     def file_read(self,file_path):
 3         pass
 4 
 5     def file_update(self,file_path):
 6         pass
 7 
 8     def file_delete(self,file_path):
 9         pass
10 
11     def file_add(self,file_path):
12         pass
13 
14 class Excel:
15     def excel_read(self,file_path):
16         pass
17 
18     def excel_update(self,file_path):
19         pass
20 
21     def excel_delete(self,file_path):
22         pass
23 
24     def excel_add(self,file_path):
25         pass

提取公共值

 1 class File:
 2     def __init__(self,file_path):
 3         self.file_path = file_path
 4                             
 5     def file_read(self):
 6         pass
 7 
 8     def file_update(self):
 9         pass
10 
11     def file_delete(self):
12         pass
13 
14     def file_add(self):
15         pass
16 
17 class Excel:
18     def __init__(self,file_path):
19         self.file_path = file_path
20                             
21     def excel_read(self):
22         pass
23 
24     def excel_update(self):
25         pass
26 
27     def excel_delete(self):
28         pass
29 
30     def excel_add(self):
31         pass

# 将相同的参数封装在构造函数里，每个方法不需要传参

方法二：在指定的类中编写和当前类相关的所有代码+提取公共值

 1 class Message:
 2     def email(self):    
 3     pass 
 4                 
 5 class Person:
 6     def __init__(self,na, gen, age, fig)
 7         self.name = na
 8         self.gender = gen
 9         self.age = age
10         self.fight =fig
11                         
12         def grassland(self):    
13         self.fight = self.fight - 10  
14                         
15     def practice(self):
16         self.fight = self.fight + 90   
17                         
18     def incest(self):
19         self.fight = self.fight - 666
20                         
21                 
22 cang = Person('刘安', '女', 18, 1000)   
23 dong = Person('李静', '男', 20, 1800)  
24 bo = Person('张华', '女', 19, 2500)      
25             
26 dong.grassland()

二、面向对象的三大特性：分装、继承、多态
1、封装

1 # 将相关功能封装到一个类中:
2 class Message:
3     def email(self):pass
4     def msg(self):pass
5     def wechat(self):pass

1 # 将数据分装到一个对象中：
2 class Person:
3     def __init__(self,name,age,gender):
4         self.name = name
5         self.age = age
6         self.gender = gender
7                         
8 obj = Person('李静',18,'女')

2、继承，提高代码的重用性
一个子类可以继承多个父类，当调用的方法在子类里没有时，到父类的方法找，如果有则调用

 1 class SuperBase:
 2     def f3(self):
 3         print('f3')
 4 
 5 class Base(SuperBase):  # 父类,基类
 6     def f2(self):
 7         print('f2')
 8 
 9 class Foo(Base):        # 子类,派生类
10                     
11     def f1(self):
12         print('f1')
13                         
14 obj = Foo()
15 obj.f1()
16 obj.f2()
17 obj.f3()

关于继承的查找顺序

练习1

 1 class Base1:
 2     def f1(self):
 3         print("base1.1")
 4     def f2(self):
 5         print("base1.f2")
 6     def f3(self):
 7         print("base1.f3")
 8 class Base2:
 9     def f1(self):
10         print("base2.f1")
11 class Foo(Base1,Base2):
12     def f0(self):
13         print("f00.f0")
14         self.f3()

练习2

 1 class Base1:
 2     def f1(self):
 3         print("base1.1")
 4     def f2(self):
 5         print("base1.f2")
 6     def f3(self):
 7         print("base1.f3")
 8 class Base2:
 9     def f1(self):
10         print("base2.f1")
11 class Foo(Base1,Base2):
12     def f0(self):
13         print("f00.f0")
14         self.f3()
15 
16 obj=Foo()
17 obj.f0()