Error in the recognition script.py

I have an error when executing the promo code.py, I'm doing facial recognition, I already capture the faces I want the problem is the error in a line and honestly I do not know how to fix attached image and the script made in python waiting for your prompt help or answer, the error comes out on line 55, on the variable face

Script code

ys, numpy, os
size = 4
fn_haar = 'haarcascade_frontalface_alt.xml'
fn_dir = 'att_faces/orl_faces'

# Part 1: Creando fisherRecognizer
print('Formando...')
# Crear una lista de imagenes y una lista de nombres correspondientes
(images, lables, names, id) = ([], [], {}, 0)
for (subdirs, dirs, files) in os.walk(fn_dir):
    for subdir in dirs:
        names[id] = subdir
        subjectpath = os.path.join(fn_dir, subdir)
        for filename in os.listdir(subjectpath):
            path = subjectpath + '/' + filename
            lable = id
            images.append(cv2.imread(path, 0))
            lables.append(int(lable))
        id += 1
(im_width, im_height) = (112, 92)

# Crear una matriz Numpy de las dos listas anteriores
(images, lables) = [numpy.array(lis) for lis in [images, lables]]
# Line24
# OpenCV entrena un modelo a partir de las imagenes
model = cv2.createFisherFaceRecognizer()
model.train(images, lables)

# Part 2: Utilizar fisherRecognizer en funcionamiento la camara
haar_cascade = cv2.CascadeClassifier(fn_haar)
webcam = cv2.VideoCapture(0)
while True:
    (rval, frame) = webcam.read()
    frame=cv2.flip(frame,1,0)
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    mini = cv2.resize(gray, (gray.shape[1] / size, gray.shape[0] / size))
    faces = haar_cascade.detectMultiScale(mini)
    for i in range(len(faces)):
        face_i = faces[i]
        (x, y, w, h) = [v * size for v in face_i]
        face = gray[y:y + h, x:x + w]
        face_resize = cv2.resize(face, (im_width, im_height))

        # Intentado reconocer la cara
        prediction = model.predict(face_resize)
        cv2.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 3)
        # LIne47
        # Escribiendo el nombre de la cara reconocida
        # [1]
        if prediction[1]<500:
     cv2.putText(frame,
          '%s - %.0f' % (names[prediction[0]],prediction[1]),
          (x-10, y-10), cv2.FONT_HERSHEY_PLAIN,1,(0, 255, 0))
   #LIne 54 La variable cara tendra el nombre de la persona reconocida  
   cara = '%s' % (names[prediction[0]])
   #Encender led en caso de que la cara se de miguel
   if cara == "Sergio":
    os.system("/home/pi/recoFacial/Sergio.sh")
   # Si la cara es desconocida, poner desconocido
   else:
     cv2.putText(frame,
          'Desconocido',
           (x-10, y-10), cv2.FONT_HERSHEY_PLAIN,1,(0, 255, 0))

   os.system("/home/pi/recoFacial/nadie.sh")
    cv2.imshow('OpenCV', frame)
    key = cv2.waitKey(10)


    if key == 27:
        break