详解Python中 __get__和__getattr__和__getattribute__的区别
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引子
如果以上都搜不到,则抛AttributeError异常. ps.从上面可以看到,dot(.)操作是昂贵的,很多的隐式调用,特别注重性能的话,在高频的循环内,可以考虑绑定给一个临时局部变量.
class C(object):
def __setattr__(self,name,value):
print "__setattr__ called:",value
object.__setattr__(self,value)
def __getattr__(self,name):
print "__getattr__ called:",name
def __getattribute__(self,name):
print "__getattribute__ called:",name
return object.__getattribute__(self,name)
c = C()
c.x = "foo"
print c.__dict__['x']
print c.x
2.object.__getattribute__(self,name) 3.object.__get__(self,instance,owner)
class C(object):
a = 'abc'
def __getattribute__(self,*args,**kwargs):
print("__getattribute__() is called")
return object.__getattribute__(self,**kwargs)
# return "haha"
def __getattr__(self,name):
print("__getattr__() is called ")
return name + " from getattr"
def __get__(self,owner):
print("__get__() is called",owner)
return self
def foo(self,x):
print(x)
class C2(object):
d = C()
if __name__ == '__main__':
c = C()
c2 = C2()
print(c.a)
print(c.zzzzzzzz)
c2.d
print(c2.d.a)
输出结果是： __getattribute__() is called abc __getattribute__() is called __getattr__() is called zzzzzzzz from getattr __get__() is called <__main__.C2 object at 0x16d2310> <class '__main__.C2'> __get__() is called <__main__.C2 object at 0x16d2310> <class '__main__.C2'> __getattribute__() is called abc 小结： 可以看出，每次通过实例访问属性，都会经过__getattribute__函数。而当属性不存在时，仍然需要访问__getattribute__，不过接着要访问__getattr__。这就好像是一个异常处理函数。 需要注意的是，当使用类访问不存在的变量是，不会经过__getattr__函数。而descriptor不存在此问题，只是把instance标识为none而已。 （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |