opencv:试图从摄像头代码中了解捕获视频

下面是从opencv文档到打开和关闭网络摄像头的简单代码,

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # Our operations on the frame come here
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

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

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

问题:

1)上述代码中的use numpy库是什么,为什么需要它?

2)如何查看 cv2.waitKey(0) ?