Python OpenCV: ValueError: too many values to unpack

Question

I am trying to get through an OpenCV tutorial and I am using the provided source code. I run into this error:

File "C:\xxx\xxxxxxx\Desktop\basic-motion-detection\motion_detector.py", line 61, in cv2.CHAIN_APPROX_SIMPLE) ValueError: too many values to unpack.

Here is the code:

# on thresholded image
thresh = cv2.dilate(thresh, None, iterations=3)
(cnts, _) = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL,
    cv2.CHAIN_APPROX_SIMPLE)`

Possible duplicate of OpenCV python: ValueError: too many values to unpack — Dan Mašek
– Dan Mašek, Commented Oct 9, 2017 at 19:16
Looks like you're using OpenCV 3.x (next time, please specify the version), yet writing code intended for 2.x. Some of the API has changed. If in doubt, you can always use help. — Dan Mašek
– Dan Mašek, Commented Oct 9, 2017 at 19:23
Also see stackoverflow.com/questions/20851365/…, where the user had the opposite problem. — Warren Weckesser
– Warren Weckesser, Commented Oct 9, 2017 at 20:30

roccolocko · Accepted Answer · 2017-10-09 23:37:53Z

3

The problem is that you are using cv2 version 3, and not version 2, the code is for version 2. To Solve your problem only change this line

(cnts, _) = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL,
    cv2.CHAIN_APPROX_SIMPLE)

for this:

(_, cnts, _) = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL,
    cv2.CHAIN_APPROX_SIMPLE)

answered Oct 9, 2017 at 23:37

roccolocko

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