python中的__init__ 、__new__、__call__等内置函数的剖析

1.__new__(cls, *args, **kwargs)  

创建对象时调用,返回当前对象的一个实例;注意:这里的第一个参数是cls即class本身
2.__init__(self, *args, **kwargs)

创建完对象后调用,对当前对象的实例的一些初始化,无返回值,即在调用__new__之后,根据返回的实例初始化;注意,这里的第一个参数是self即对象本身【注意和new的区别】
3.__call__(self,  *args, **kwargs)

如果类实现了这个方法,相当于把这个类型的对象当作函数来使用,相当于 重载了括号运算符

#__conding:utf-8__

class Person:
def __init__(self, name):
self.name = name
def sayHi(self):
print("Hello my name is:%s" %self.name) p = Person("wuyanlong")
p.sayHi() class P(object):
def __init__(self, *args, **kwargs):
print "init"
super(P,self).__init__(*args, **kwargs)
def __new__(cls, *args, **kwargs):
print "new", cls
return super(P, cls).__new__(cls ,*args, **kwargs)
def __call__(self, *args, **kwargs):
print "call" pp = P()
print "__________"
pp()

运行结果:

***:~/Python爬虫/class$ python calss1.py
Hello my name is:wuyanlong
new <class '__main__.P'>
init
__________
call

4. __getattr__:

从对象中读取某个属性时,首先需要从self.__dicts__中搜索该属性,再从__getattr__中查找。

class A(object):
def __init__(self):
self.name = 'from __dicts__: zdy' def __getattr__(self, item):
if item == 'name':
return 'from __getattr__: zdy'
elif item == 'age':
return 26 a = A()
print a.name # 从__dict__里获得的
print a.age # 从__getattr__获得的

5. __setattr__

class A(object):
def __setattr__(self, *args, **kwargs):
print 'call func set attr'
return object.__setattr__(self, *args, **kwargs)

6. __delattr__

函数式用来删除对象的属性:

class A(object):
def __delattr__(self, *args, **kwargs):
print 'call func del attr'
return object.__delattr__(self, *args, **kwargs)
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