Built-in functions __str__ and __del__

1. What is a built-in function: the functions defined in the class in the form of __function name__, these functions will be executed spontaneously under specific circumstances.

Second, the role of built-in functions: special objects can be customized when creating objects.

Third, the built-in function __str__: It will be automatically triggered when the object is printed, and then the return value obtained by calling this function will be printed as the content.

class Human:
     DEF  the __init__ (Self, name, Age): 
        the self.name = name 
        self.age = Age 
obj = Human ( ' Tom ' , ' 18 is ' )
 Print (obj)   # class vivo undefined __str__, will by default __str__ parent class object is performed, the result is <__ __ main object Human AT 0x0000022CAE9E45E0.> 

class Human:
     DEF  the __init__ : (Self, name, Age) 
        the self.name = name 
        self.age = Age
     DEF  __str__ (Self):
        return the self.name   # customized __str__, to return the object 'name' attribute value 
obj = Human ( ' Tom ' , ' 18 is ' )
 Print (obj)   # print target, i.e., printing a return __str__ Value, which is the value of the object's 'name' attribute, the result is tom

Fourth, the built-in function __del__: When clearing an object, the function is triggered before the operation of clearing the object.

class Human:
     DEF  the __init__ (Self, name, Age): 
        the self.name = name 
        self.age = Age
     DEF  the __del__ (Self):
         Print ( ' delete your sister ' ) 
obj = Human ( ' Tom ' , ' 18 is ' )
 del obj
 Print ( ' program coming to an end ' )
 # triggers __del__ function inside the class definition before deleting obj, the result is delete your sister ===> program near the end of 

class Human:
     DEF  __init__(Self, name, Age): 
        self.name = name 
        self.age = Age
     DEF  __del__ (Self):
         Print ( ' delete your sister ' ) 
obj = Human ( ' tom ' , ' 18 ' )
 Print ( ' program coming to an end ' )
 # automatically at the end of the recovery is not manually delete obj obj program memory, it will also trigger __del__ function, the result is a program coming to an end ===> delete your sister 

class Human:
     DEF  __init__ (Self, name, Age ): 
        self.name = name
        self.age= Age 
        self.f = Open (r ' 00 notes .txt ' , ' rb ' )   # object created will be a file handle attribute 
    DEF  __del__ (Self): 
        self.f.close ()   # Since the end of the program only Reclaim the application's memory resources, the system's memory usage will not be automatically released, so here you need to customize the __del__ function to automatically release the system memory usage at the end of the program