def _instance_callable(obj):
    """Given an object, return True if the object is callable.
    For classes, return True if instances would be callable."""
    if not isinstance(obj, ClassTypes):
        # already an instance
        return getattr(obj, '__call__', None) is not None

    if six.PY3:
        # *could* be broken by a class overriding __mro__ or __dict__ via
        # a metaclass
        for base in (obj,) + obj.__mro__:
            if base.__dict__.get('__call__') is not None:
                return True
    else:
        klass = obj
        # uses __bases__ instead of __mro__ so that we work with old style classes
        if klass.__dict__.get('__call__') is not None:
            return True

        for base in klass.__bases__:
            if _instance_callable(base):
                return True
    return False