[ INFO:0] Initialize OpenCL runtime...
OpenCV(3.4.1) Error: Assertion failed (K == 1 && update == 0 && mask.empty()) in
cv::batchDistance, file D:\Build\OpenCV\opencv-3.4.1\modules\core\src\batch_dis
tance.cpp, line 265
Traceback (most recent call last):
File "test_3.py", line 13, in
matches = bf.knnMatch(des1,des2,k=2)
cv2.error: OpenCV(3.4.1) D:\Build\OpenCV\opencv-3.4.1\modules\core\src\batch_dis
tance.cpp:265: error: (-215) K == 1 && update == 0 && mask.empty() in function c
v::batchDistance