python3 TypeError: Incorrect type of self (must be 'Feature2D' or its derivative)

问题：在用python3使用orb = cv2.ORB()进行ORB时候，可能会产生错误：TypeError: Incorrect type of self (must be 'Feature2D' or its derivative)

import numpy as np
import cv2
from matplotlib import pyplot as plt
img1 = cv2.imread('data/queryImage.jpg', 0)  # queryImage
img2 = cv2.imread('data/trainImage.jpg', 0)  # trainImage
# Initiate SIFT detector
orb = cv2.ORB()
# find the keypoints and descriptors with SIFT
kp1, des1 = orb.detectAndCompute(img1, None)
kp2, des2 = orb.detectAndCompute(img2, None)

报错信息：

TypeError                                 Traceback (most recent call last)
 in ()
      3 
      4 # find the keypoints and descriptors with ORB
----> 5 kp1, des1 = orb.detectAndCompute(img1,None)
      6 kp2, des2 = orb.detectAndCompute(img2,None)
      7 

TypeError: Incorrect type of self (must be 'Feature2D' or its derivative)

解决：将orb = cv2.ORB()替换为：orb = cv2.ORB_create()

分析：

        在opencv2中， orb = cv2.ORB ()是对的；
        在opencv3中这样会报错，改成orb = cv2.ORB_create()就没问题了。

变更样例：

import numpy as np
import cv2
from matplotlib import pyplot as plt
img1 = cv2.imread('data/queryImage.jpg', 0)  # queryImage
img2 = cv2.imread('data/trainImage.jpg', 0)  # trainImage
# Initiate SIFT detector
#orb = cv2.ORB()  将orb= cv2.ORB()替换为：orb= cv2.ORB_create()
orb= cv2.ORB_create()
# find the keypoints and descriptors with SIFT
kp1, des1 = orb.detectAndCompute(img1, None)
kp2, des2 = orb.detectAndCompute(img2, None)

说明：问题产生的环境
  Python版本：3.6.5
  OpenCV版本：3.4.2