videocapture(0) and .read returning false every time

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i have been trying this code, but the ret value is returning false everytime due to which i am unable to load video from my laptop camera please help:

import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):  # check !
    # capture frame-by-frame

    ret, frame = cap.read()
    print(ret)

    if ret: # check ! (some webcam's need a "warmup")
        # our operation on frame come here
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

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

    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
# When everything is done release the capture
cap.release()
cv2.destroyAllWindows()