内置方法

1. 什么是内置方法

## 定义在类内部，以__开头和__结尾的方法称之为内置方法

## 会在满足某种情况下回自动触发执行
## 为什么用： 为了定制化我们的类或者对象

2. 如何使用内置方法

# __str__
# __del__

class People:
    def __init__(self,name,age):
        self.name = name
        self.age = age
        
    def say(self):
        print('<%s:%s>'%(self.name,self.age))

obj = People('yanchen',18)
print(obj)  ## <__main__.People object at 0x00000276F6B8B730>

## ----------------------------------------------------------------------

## __str__ 来完成定制化操作
class People:
    def __init__(self,name,age):
        self.name = name
        self.age = age
        
    def say(self):
        print('<%s:%s>'%(self.name,self.age))
    
    def __str__(self):
        print('这是xxxxx对象')   ## 值起到提示作用
        return '<%s:%s>' % (self.name, self.age)  ## 必须要有return，而且返回字符串

obj = People('yanchen',18)
print(obj)  ##  <yanchen:18>

## ----------------------------------------------------------------------------------------
# __del__ :在清理对象时触发，会先执行该方法

class People:
    def __init__(self,name,age):
        self.name = name
        self.age = age
        
    def say(self):
        print('<%s:%s>'%(self.name,self.age))
        
    def __del__(self):
        print('running......')

obj = People('yanchen',18)
print('=======================')

'''
 == == == == == == == == == == == =    ## 程序运行完了，要清理对象
running......  ## 清理对象时云运行
'''

## ---------------------------------------------------------------------------------------
class People:
    def __init__(self,name,age):
        self.name = name
        self.age = age
        
    def say(self):
        print('<%s:%s>'%(self.name,self.age))
        
    def __del__(self):
        print('running......')

obj = People('yanchen',18)
del obj
print('=======================')

'''
running......  ## 清理对象时云运行
 == == == == == == == == == == == =    ## 程序运行完了
'''

## ---------------------------------------------------------------------------------------------
#####  对象本身占得是应用程序的内存空间，所以没有多大用处

##### 但是如果对象某个属性x 比如 obj.x 占得是操作系统内存空间，对象运行完了以后Python回收的是程序中的内存空间
### 操作系统不会被回收

class People:
    def __init__(self,name,age):
        self.name = name
        self.age = age
        self.x = open('yanchen.txt','w',encoding="utf-8")
        
    def say(self):
        print('<%s:%s>'%(self.name,self.age))
        
    def __del__(self):
        print('running......')
        ## 发起系统调用，告诉系统回收操作系统资源,比如如下：
        self.x.close()

obj = People('yanchen',18)
print('=======================')