python的描述符(descriptor)、装饰器（property）造成的一个无限递归问题分享

# coding: utf-8

class A(object):

    @property
    def _value(self):
#        raise AttributeError("test")
        return {"v": "This is a test."}

    def __getattr__(self, key):
        print "__getattr__:", key
        return self._value[key]

if __name__ == '__main__':
    a = A()
    print a.v

__getattr__: v
This is a test.

#        raise AttributeError("test")

File "attr_test.py", line 12, in __getattr__
    return self._value[key]
  File "attr_test.py", line 12, in __getattr__
    return self._value[key]
RuntimeError: maximum recursion depth exceeded while calling a Python object

object.__get__(self, instance, owner)

Called to get the attribute of the owner class (class attribute access) or of an instance of that class (instance attribute access). owner is always the owner class, while instance is the instance that the attribute was accessed through, or None when the attribute is accessed through the owner. This method should return the (computed) attribute value or raise an AttributeError exception.