我得到一个导入错误：没有名为cv2的模块

Question

我已经在我的raspberry pi上安装了python3.5、opencv3.3.0和numpy20.2.4，请参阅https://www.pyimagesearch.com/2017/09/04/raspbian-stretch-install-opencv-3-python-on-your-raspberry-pi/。但一旦我尝试跑步。它显示导入错误：没有名为cv2的模块。有人可以帮忙。我是新来的。多谢各位

import numpy as np 
import cv2

cap = cv2.VideoCapture(0)
cap = set(3,640) #set Width
cap = set(4,480) #set Height

while(True):
    ret, frame = cap.read()
    frame =  cv2.flip(frame, -1) # flip camera vertically
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    
    cv2.imshow ('frame',frame)
    cv2.imshow ('gray',gray)
    
    k = cv2.waitKey(30) &0xff
    if k == 27: #press  ESC to exit
        break

cap.release()
cv2.destroyAllWindows()

错误：

Traceback (most recent call last):
  File "Face_recognition.py", line 2, in <module>
    import cv2
ImportError: No module named cv2