'Begin playback, possibly at a specified playlist index.'

def cmd_play(self, conn, index=(-1)):

    index = cast_arg(int, index)
    if ((index < (-1)) or (index > len(self.playlist))):
        raise ArgumentIndexError()
    if (index == (-1)):
        if (not self.playlist):
            return self.cmd_stop(conn)
        if (self.current_index == (-1)):
            self.current_index = 0
    else:
        self.current_index = index
    self.paused = False
