def is_function(self):
        """return True if callback is a vanilla plain jane function"""
        if self.is_instance() or self.is_class(): return False
        return isinstance(self.callback, (Callable, classmethod))
def is_function(self):
        """return True if callback is a vanilla plain jane function"""
        if self.is_instance() or self.is_class(): return False
        return isinstance(self.callback, (Callable, classmethod))
return True if callback is a vanilla plain jane function