Now that callable() is back in 3.2, we may replace hasattr(obj, '__call__') with callable(obj).

The built-in function is easier to read and gives better performance than attribute lookup.


$ ./python -m timeit "hasattr(None, '__call__')"
100000 loops, best of 3: 4.09 usec per loop
$ ./python -m timeit "hasattr(str, '__call__')"
1000000 loops, best of 3: 1.3 usec per loop

$ ./python -m timeit "callable(None)"
1000000 loops, best of 3: 0.299 usec per loop
$ ./python -m timeit "callable(str)"
1000000 loops, best of 3: 0.369 usec per loop

Proposed patch.

For packaging I'm not sure it's worth complicating backporting.

Updated with a special note for "packaging".

callable() is not just faster, it's also "more correct": hasattr(obj, "__call__") doesn't call base classes. See callable() of the six module:


def callable(obj):
  return any("__call__" in klass.__dict__ for klass in type(obj).__mro__)

We have so many alternatives, it's funny ...


def callable(obj):
    return hasattr(obj, '__call__') or hasattr(obj, '__bases__')

def callable(obj):
    return isinstance(obj, collections.abc.Callable)

def callable(obj):
    return hasattr(obj, '__call__') or type(obj) == types.ClassType

def callable(obj):
    return any("__call__" in klass.__dict__
               for klass in type(obj).__mro__)

Is it actually appropiate to commit this to 3.2?. I am neutral to it, just asking.

> Is it actually appropiate to commit this to 3.2?

If it fixes a bug, the fix should be backported to 3.2.

This change is fine for packaging.  In the 2.x backport I already use callable (and damn the py3k warning) and  the 3.x backport uses the incorrect hasattr(inst, '__call__'); I’ll change that to use a backported d2.compat.callable.

New changeset 8e57b5d8f58f by Florent Xicluna in branch '3.2':
Closes #13258: Use callable() built-in in the standard library.
http://hg.python.org/cpython/rev/8e57b5d8f58f