hasattr(x, '__call__') has been suggested as a replacement for
callable(x) in the documentation and in the warning when running
python2.6 with -3. It is also what 2to3 replaces it with. However, the
two are not equivalent.

1. I can add a __call__ attribute to my object with "obj.__call__ =
lambda x:x". That will not make the object callable, callable() on
Python 2.6 returns False, but hasattr(obj, '__call__') returns True.
2. I can implement a __getattr__ that returns something for every
possible attribute name. Again, this doesn't make the object callable,
nor does callable(obj) in Python 2.6 return True.

I think a closer replacement for "callable(x)" would be "'__call__' in
vars(type(x))".