Hi, I found a tiny typo in documentation but I don't know how to correct it. In the link below, http://docs.opencv.org/trunk/doc/py_tutorials/py_calib3d/py_calibration/py_calibration.html#calibration
I believe in the "setup" chapter, cv2.drawChessboardCorners(img, (7,6), corners2,ret) has an extra '2. As I tried out myself, it should be cv2.drawChessboardCorners(img, (7,6), corners,ret).
Sure, it's not a big deal. Still hope anyone who has the access can fix that! :)