'Updates mapping for the signal to the message\'s control change.
Args:
signal: The name of the signal to update the control change for.
msg: The mido.Message whose control change the signal should be set to.'

def _update_signal(self, signal, msg):

    if (msg.control in self._cc_map.values()):
        print ('Control    number    %d    is    already    assigned.    Ignoring.' % msg.control)
    else:
        self._cc_map[signal] = msg.control
        print ('Assigned    control    number    %d    to    `%s`.' % (msg.control, signal))
    self._update_event.set()
