Failure with OpenCV 4

[mvl22]

Using opencv-python-4.1.0.25, the following error is generated:

$ python pyANPD.py image.jpg 
Traceback (most recent call last):
  File "pyANPD.py", line 152, in <module>
    o1 = process_image(path, 0, type='rect')
  File "pyANPD.py", line 79, in process_image
    _,contours,_=cv2.findContours(gray, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
ValueError: need more than 2 values to unpack

This does not happen with OpenCV 3.4.5.20, i.e. use pip install opencv-python==3.4.5.20