'Appends the event to the end of the drums and increments the end step.
Args:
event: The drum event to append to the end.
Raises:
ValueError: If `event` is not a valid drum event.'

def append(self, event):

    if (not isinstance(event, frozenset)):
        raise ValueError(('Invalid    drum    event:    %s' % event))
    if (not all(((MIN_MIDI_PITCH <= drum <= MAX_MIDI_PITCH) for drum in event))):
        raise ValueError(('Drum    event    contains    invalid    note:    %s' % event))
    super(DrumTrack, self).append(event)
