detect face using opencv with webcam

face_detect.py

def objectTracker1(cascPath):
    
    faceCascade = cv2.CascadeClassifier(cascPath)
    
    cv2.namedWindow("preview")
    vc = cv2.VideoCapture(0)
    
    while True: # try to get the first frame
        rval, frame = vc.read()
        # Capture frame-by-frame
        ret, frame = vc.read()
        
        #Convert frame to grayscale
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    
        objects = faceCascade.detectMultiScale(gray, scaleFactor=1.2, 
                                               minNeighbors=1, minSize=(40, 40), 
                                               flags=cv2.CASCADE_SCALE_IMAGE)
        # Draw a rectangle around the faces
        for (x, y, w, h) in objects:
            cv2.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)
        
        cv2.imshow("preview", frame)
        rval, frame = vc.read()
        key = cv2.waitKey(20)
        if key == 27: # exit on ESC
            break

    vc.release()
    cv2.destroyWindow("preview")