True if the object is a callable that takes no arguments.

def is_simple_callable(obj):
    """
    True if the object is a callable that takes no arguments.
    """
    function = inspect.isfunction(obj)
    method = inspect.ismethod(obj)

    if not (function or method):
        return False

    args, _, _, defaults = inspect.getargspec(obj)
    len_args = len(args) if function else len(args) - 1
    len_defaults = len(defaults) if defaults else 0
    return len_args <= len_defaults