特征点识别问题，为什么出现错误

[3icr]

sensor.skip_frames(time = 2000)

sensor.set_auto_gain(False, value=100)


def draw_keypoints(img, kpts):

    if kpts:

        print(kpts)

        img.draw_keypoints(kpts)

        img = sensor.snapshot()

        time.sleep(1000)
        

kpts1 = image.load_descriptor("/zhixing.orb")

kpts2 = image.load_descriptor("/youzhaun.orb")

kpts3 = image.load_descriptor("/zuozhuan.orb")

clock = time.clock()

while (True):

    clock.tick()

    img = sensor.snapshot()

    kpts0 = img.find_keypoints(max_keypoints=150, threshold=10, normalized=True)

    if (kpts1):

        match = image.match_descriptor(kpts0,kpts1,threshold=85)

        if (match.count()>10):

            img.draw_rectangle(match.rect())

            img.draw_cross(match.cx(), match.cy(), size=10)
            print(1)
                
    
    if (kpts2): 
    
        match = image.match_descriptor(kpts0, kpts2,threshold=85)
        
        if (match.count()>10):
             
            img.draw_rectangle(match.rect())
                  
            img.draw_cross(match.cx(), match.cy(), size=10)
                  
    if (kpts3): 
        match = image.match_descriptor(kpts0, kpts2, threshold=85)
        
        if (match.count()>10):
        
            img.draw_rectangle(match.rect())

程序出现错误