(self, fn, signal)
Calls `fn` at the next signal message.

    The callback function must take exactly one argument, which will be the
    message triggering the signal.

    Survives until signal is called or the MidiHub is destroyed.

    Args:
      fn: The callback function to call, passing in the triggering message.
      signal: A MidiSignal to use as a signal to call `fn` on the triggering
          message.
Calls `fn` at the next signal message.
Calls fn at the next signal message .
def register_callback(self, fn, signal):
    """Calls `fn` at the next signal message.

    The callback function must take exactly one argument, which will be the
    message triggering the signal.

    Survives until signal is called or the MidiHub is destroyed.

    Args:
      fn: The callback function to call, passing in the triggering message.
      signal: A MidiSignal to use as a signal to call `fn` on the triggering
          message.
    """
    self._callbacks[re.compile(str(signal))].append(fn)
def register_callback ( self , fn , signal ) : self . _callbacks [ re . compile ( str ( signal ) ) ] . append ( fn )