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the problem is here:

image, contours, heirarchy = cv2.findContours(edged, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

this will replace your 3 channels image with a 1 channel one, and you cannot draw something green into that (it'll be invisible)

instead, try:

_, contours, heirarchy = cv2.findContours(edged, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

now drawContours should work as expected ;)