Python入门：面向对象之典型魔术方法

在Python中，所有以“__”双下划线包起来的方法，如__init__，称为“Magic Method”，中文称魔术方法。下面简要介绍典型的魔术方法：

初始化__init__、构造__new__、析构__del__

<code>
class
 
Person
:
    
def
 
__init__
(
self
, name):
        
self
.name = name
        print(
'%s __init__ method running...'
 % 
self
)

    
def
 
__new__
(cls, *args, **kwargs)
:
        new_object = 
super
().__new_
_
(cls)
        print(
'__new__ method running and create new object: %s ...'
 % new_object)
        
return
 new_object

    
def
 
__del__
(
self
):
        print(
'%s __del__ method running...'
 % 
self
)


jack = Person(
'jack'
)/<code>

结果：

__new__ method running and create new object: ...

__init__ method running...

__del__ method running...

解释：

1. 执行__new__方法生成对象，返回值是该对象
2. 执行__init__方法完成初始化，丰富该对象
3. 对象生命周期结束或程序结束，执行__del__析构函数

__str__

自定义对象的字符串表示。

<code>
class
 
Person
:
    
def
 
__str__
(
self
):
        print(
'__str__ running...'
)
        
return
 
self
.name + 
'--'
 + 
self
.gender + 
'--'
 + 
self
.age

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

jack = Person(
'jack'
, 
'male'
, 
'18'
)
print(jack)/<code>

结果：

__str__ running...

jack--male--18

__dict__

<code>
class
 
Person
:
    gender = 
'male'
    
def
 
__init__
(self, name)
:
        self.name = name
 
    
def
 
clazz_func
(cls)
:
        
pass
 
    
def
 
static_fuc
()
:
        
pass
    
def
 
func
(self)
:
        
pass

print(Person.__dict__)  
jack = Person(
'jack'
)
print(jack.__dict__) /<code>

结果：

{'__module__': '__main__',

'gender': 'male',

'__init__': ,

'clazz_func': ,

'static_fuc': ,

'func': ,

'__dict__': ,

'__weakref__': ,

'__doc__': None}

{'name': 'jack'}

__getattr__

当查找不到对象属性时调用，这里查找的范围是对象本身及类的__dict__键对应的值。

<code>
class
 
Person
:
    
gender = 'male'

jack = Person()
print(jack.name)  # AttributeError: 
'Person'
 
object
 has no attribute 
'name'
/<code>

<code>
class
 
Person
:
    
def
 
__getattr__
(self, item)
:
        
return
 
'不能找到'
 + item + 
'项。'

jack = Person()
print(jack.name)  
print(jack.__doc__) /<code>

__setattr__

<code>
class
 
Person
:
    
def
 
__setattr__
(self, key, value)
:
        print(
'__setattr_ running..'
)
        self.__dict__[key] = value   

jack = Person()
jack.name = 
'jack'
print(jack.name)/<code>

结果：

__setattr_ running..

jack

__delattr__

<code>
class
 
Person
:
    
def
 
__delattr__
(self, item)
:
        print(
'__delattr__ running.'
)
        self.__dict__.pop(item)  

jack = Person()
jack.name = 
'jack'
del
 jack.name  
print(jack.name) /<code>

關鍵字: def print Person