I just spend a while tracking down a bug in my code which turned out to be an unexpected behaviour of hasattr.

Running this

class Test(object):
    def __init__(self):
        self.__private = "Hello"
    def test(self):
        print(self.__private)
        print(hasattr(self, "__private"))
        print(getattr(self, "__private"))


t = Test()
t.test()

Prints

>>> t.test()
Hello
False
Traceback (most recent call last):
  File "private_test.py", line 10, in <module>
    t.test()
  File "private_test.py", line 7, in test
    print(getattr(self, "__private"))
AttributeError: 'Test' object has no attribute '__private'
>>>

Indicating that even though we just printed self.__private hasattr() can't find it nor getattr().

I think this is probably the intended behaviour, but it does seem inconsistent.

Probably all that is required is a documentation patch...

Maybe something add something like this to the end of

  http://docs.python.org/library/functions.html#hasattr

Note that hasattr won't find private (double underscore) attributes unless the mangled name is used.