module 'cv2.cv2' has no attribute 'cv'

错误原因：opencv版本问题，改为opencv 3的代码就可以了

碰到的代码错误：

cap = cv2.VideoCapture(0)
fourcc = cv2.cv.FOURCC(*'XVID')
out = cv2.VideoWriter('output.avi', fourcc, 20.0, (640, 480))

修改：

fourcc = cv2.VideoWriter_fourcc(*'XVID')