Why does faceCascade.detectMultiScale abort on call?

edit

The code is:

import cv2
import sys

cascPath = sys.argv[1]
faceCascade = cv2.CascadeClassifier(cascPath)

video_capture = cv2.VideoCapture(1)

while True:
    # Capture frame-by-frame
    ret, frame = video_capture.read()

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    faces = faceCascade.detectMultiScale(
        gray,
        scaleFactor=1.1,
        minNeighbors=5,
        minSize=(30, 30),
        flags=cv2.CASCADE_SCALE_IMAGE
    )

    # Draw a rectangle around the faces
    for (x, y, w, h) in faces:
        cv2.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)

    # Display the resulting frame
    cv2.imshow('Video', frame)

    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything is done, release the capture
video_capture.release()
cv2.destroyAllWindows()

Code was from https://realpython.com/blog/python/fa...

The original code did not work because of deprication of cv2.cv.CV_HAAR_SCALE_IMAGE which is replaced with cv2.CASCADE_SCALE_IMAGE from guidance at https://stackoverflow.com/questions/4...

However, cv::CascadeClassifier::detectMultiScale causes exception with assertion (!empty()) at cascadedetect.cpp line 1681

I am using windoze 10, OpenCV 3.2, Python 2.7.9 64bit (stackless)

Any ideas please? It is a fresh install of OpenCV binaries.

Cheers, B