human
Solve the following python programming problem given the following code:
def add_io_state(self, state) : 
    'Add IO state to the eventloop.

        Parameters
        ----------
        state : zmq.POLLIN|zmq.POLLOUT|zmq.POLLERR
            The IO state flag to set.

        This is thread safe as it uses the thread safe IOLoop.add_callback.
        ' 
    def add_io_state_callback() : 
        if (not (self.iostate & state)) : 
            self.iostate = (self.iostate | state) 
            self.ioloop.update_handler (self.socket, self.iostate) 
self.ioloop.add_callback (<MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def add_io_state_callback(