python pygame 时钟钟摆

if y == 300 and x != 100:
    x -= 100
    print(' x -= 100')
elif x == 100 and y != 100:
    y -= 100
    print(' y -= 100')

elif y == 100 and x != 300:
    x += 100
    print(' x += 100')
elif x == 300 and y != 300:
    y += 100
    print(' y += 100')
print(x,y)