Python Cv2的说法是；“发现照相机”；即使不是

我正在尝试制作一个程序，如果它检测到输入，就会自动启动显示视频。但它仍然认为视频输入在那里，即使相机没有连接，它应该在我连接外部相机后立即显示视频，但它没有

这是我的代码：

import numpy as np
import cv2

ImageSource = 1
cap1 = cv2.VideoCapture(ImageSource) 

def testDevice(source): #this is to make the auto show feature.
while (True):
    if (cap1.isOpened):
      print('got video output')
      break


testDevice(ImageSource)

if (cap1.isOpened):
while(cap1.isOpened):
    # Capture frame-by-frame
    ret, frame = cap1.read()

    # Display the resulting frame
    cv2.imshow('frame', frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap1.release()
cv2.destroyAllWindows()