OpenCV Python Script Mac "aborts"

edit

So I'm just trying to run the basic OpenCV program

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

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

    # Our operations on the frame come here
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2BGRA)

    # Display the resulting frame
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

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

But for some reason when I try to run it (with python 2 or 3) I get this weird abort statement

[1]    74309 abort      python3 index.py

(I'm guessing the 5 digit number is the PID) However, it does work if I pass in a path to an already existing video in the VideoCapture function. I am a beginner in all of this so I'm not really sure what the problem is

Thanks :)