What is __getattr__ order in the attribute lookup chain?

Question

So in order to get rid of some boilerplate I opted to implement __getattr__ for delegating some method calls. The problem is that I also have a descriptor in the attribute lookup chain and they are not interacting as I expected. Here's the code:

class C(object):
    attr = Descriptor()

    def __getattr__(self, item):
        # just returns a method for all items that match
        # a certain pattern

Here's the problem. All the Python docs mention that __getattr__ only gets called after the usual lookup chain fails but in this case __getattr__ is always getting called ahead of attr.

So what is the proper way to have both a descriptor and __getattr__ play nice with each other?

Here's what I'm observing:

a = C()
a.attr # goes to __getattr__ instead of C.attr.__get__

Issue solved. It turns out if there is an exception that is thrown from a descriptor then the lookup jumps to __getattr__.

Answer 1

but in this case __getattr__ is always getting called ahead of attr

Sorry, I do not understand.

>>> class C(object):
    attr = property(fget = lambda self: 5)

    def __getattr__(self, item):
        # just returns a method for all items that match
        # a certain pattern

    return item

>>> C().x
'x'
>>> C().attr # attr.__get__ is called, not __getattr__
5

Could you specify what 'play nice with each other' means? A way to play nicely as I understand it: Method delegation in python