> alienList = []
for z0 in range( COLUMNS ): for z1 in range (ROWS ): alien = Alien((LEFT + z0 * DISTANCE, TOP + z1 * DISTANCE)) alienList.append(alien)
... should read: alienList = [] for z0 in range( COLUMNS ): for z1 in range (ROWS ): alien = Alien((LEFT + z0 * DISTANCE, TOP + z1 * DISTANCE)) alienList.append(alien) of course.