title: OpenCV : AttributeError: 'list' object has no attribute 'queryIdx'
body: <p>I'm using <code>OpenCV</code>, <code>SIFT</code> and <code>Homography</code> in order to detect all objects in a picture.</p>
  
  <p><strong>My global picture looks like :</strong></p>
  
  <p><a href="https://i.stack.imgur.com/HeqVQ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HeqVQ.jpg" alt="enter image description here"></a> </p>
  
  <p>And I want to detect all lamps on the picture, even if the orientation is not exactly the same between each one.</p>
  
  <p><strong>My model picture looks like :</strong></p>
  
  <p><a href="https://i.stack.imgur.com/nnN8R.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nnN8R.jpg" alt="enter image description here"></a></p>
  
  <p>I wrote this script with Python :</p>
  
  <pre><code>#-*- coding: utf-8! -*-
  
  import os, shutil
  import numpy as np
  import cv2
  
  #########################
  # SIFT descriptors part #
  #########################
  
  img1 = cv2.imread('/Users/test/Desktop/SIFT/Ville/ville.jpg',0)
  img2 = cv2.imread('/Users/test/Desktop/SIFT/Ville/lampe.jpg',0)
  
  ##########################
  # Initiate SIFT detector #
  ##########################
  
  sift = cv2.xfeatures2d.SIFT_create()
  
  kp1, des1 = sift.detectAndCompute(img1,None)
  kp2, des2 = sift.detectAndCompute(img2,None)
  
  FLANN_INDEX_KDTREE = 0
  index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5)
  search_params = dict(checks = 50)
  
  flann = cv2.FlannBasedMatcher(index_params, search_params)
  #bf = cv2.BFMatcher()
  matches = flann.knnMatch(des1,des2,k=2)
  
  good = []
  for m,n in matches :
      if m.distance &lt; 0.7*n.distance :
          good.append([m])
  
  MIN_MATCH_COUNT = 3
  
  if len(good)&gt;MIN_MATCH_COUNT:
      src_pts = np.float32([ kp1[m.queryIdx].pt for m in good ]).reshape(-1,1,2)
      dst_pts = np.float32([ kp2[m.trainIdx].pt for m in good ]).reshape(-1,1,2)
  
      M, mask = cv2.findHomography(src_pts, dst_pts, cv2.RANSAC,5.0)
      matchesMask = mask.ravel().tolist()
  
      h,w = img1.shape
      pts = np.float32([ [0,0],[0,h-1],[w-1,h-1],[w-1,0] ]).reshape(-1,1,2)
      dst = cv2.perspectiveTransform(pts,M)
  
      img2 = cv2.polylines(img2,[np.int32(dst)],True,255,3, cv2.LINE_AA)
  
  else:
      print "Not enough matches are found - %d/%d" % (len(good),MIN_MATCH_COUNT)
      matchesMask = None
  
  draw_params = dict(matchColor = (0,255,0), # draw matches in green color
                     singlePointColor = None,
                     matchesMask = matchesMask, # draw only inliers
                     flags = 2)
  
  img3 = cv2.drawMatches(img1,kp1,img2,kp2,good,None,**draw_params)
  
  plt.imshow(img3, 'grayfinal.jpg'),plt.show()
  cv2.imwrite('matches.jpg',img3)
  </code></pre>
  
  <p>I get this error :</p>
  
  <pre><code>Traceback (most recent call last):
    File "image.py", line 34, in &lt;module&gt;
      src_pts = np.float32([ kp1[m.queryIdx].pt for m in good ]).reshape(-1,1,2)
  AttributeError: 'list' object has no attribute 'queryIdx'
  </code></pre>
  
  <p>Do you have an idea ?</p>
  
  <p><strong>EDIT :</strong></p>
  
  <p>With assumed solutions, I got something which looks right. But How I could detect the others lamps on the picture ?</p>
  
  <p><a href="https://i.stack.imgur.com/3SGQ5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3SGQ5.png" alt="enter image description here"></a></p>