Python - 使用__getattribute__方法 [英] Python - Using __getattribute__ method
问题描述
我想覆盖对类中一个变量的访问,但是正常返回所有其他变量。我如何通过 __ getattribute __
?
class D(object):
def __init __
self.test = 20
self.test2 = 21
def __getattribute __(self,name):
如果name =='test':
return 0.
else:
return self .__ dict __ [name]
>>>> print D()。test
0.0
>>> print D()。test2
...
RuntimeError:超出最大递归深度cmp
由于调用同一个函数,你的 __ getattribute __
会得到递归错误。如果你使用 object
的 __ getattribute __
,它的工作原理:
class D(object):
def __init __(self):
self.test = 20
self.test2 = 21
def __getattribute __(self,name):
如果name =='test':
return 0.
else:
return object .__ getattribute __(self,name)
这是因为 object
类。通过调用 __ getattribute __
的基本版本,您可以避免之前的递归地狱。
Ipython输出, foo.py:
在[1]:from foo import *
在[2] d = D()
In [3]:d.test
Out [3]:0.0
在[4]:d.test2
Out [4]:21
更新: b
$ b
在 更多属性访问新样式类 ,他们建议这样做,以避免无限递归。
I want to override access to one variable in a class, but return all others normally. How do I accomplish this with __getattribute__
?
I tried the following (which should also illustrate what I'm trying to do) but I get a recursion error:
class D(object):
def __init__(self):
self.test=20
self.test2=21
def __getattribute__(self,name):
if name=='test':
return 0.
else:
return self.__dict__[name]
>>> print D().test
0.0
>>> print D().test2
...
RuntimeError: maximum recursion depth exceeded in cmp
You get a recursion error because you call the same function, your __getattribute__
. If you use object
's __getattribute__
instead, it works:
class D(object):
def __init__(self):
self.test=20
self.test2=21
def __getattribute__(self,name):
if name=='test':
return 0.
else:
return object.__getattribute__(self, name)
This works because object
(in this example) is the base class. By calling the base version of __getattribute__
you avoid the recursive hell you were in before.
Ipython output with code in foo.py:
In [1]: from foo import *
In [2]: d = D()
In [3]: d.test
Out[3]: 0.0
In [4]: d.test2
Out[4]: 21
Update:
There's something in the section titled More attribute access for new-style classes in the current documentation, where they recommend doing exactly this to avoid the infinite recursion.
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