[Python] close the webcam and keep running the program [duplicate]

I'm trying to turn off the webcam and start the other function, but when I try to do that, it keeps giving me an error and the other functions couldn't work. Here's the code.

import matplotlib.pyplot as plt
import numpy as np
import cv2
import time

cap = cv2.VideoCapture(0)
face_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_eye.xml')

def eye_detector():
while True:
ret, frame = cap.read()

gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
faces = face_cascade.detectMultiScale(gray, 1.3, 5)
for (x, y, w, h) in faces:
roi_gray = gray[y:y + w, x:x + w]
roi_color = frame[y:y + h, x:x + w]
eyes = eye_cascade.detectMultiScale(roi_gray, 1.3, 5 )

for (ex, ey, ew, eh) in eyes:
cv2.rectangle(roi_color, (ex, ey), (ex + ew, ey + eh), (0, 255, 0), 5)

cv2.imshow('frame', frame)

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

elif len(faces) >0 and (x == 210, y ==140):
time.sleep(10)
cap.release()
plt.show()

cap.release()
cv2.destroyAllWindows()


Here's the error Traceback (most recent call last): File "c:\project_ANNIE\project1.py", line 24, in <module> project1_module2.eye_detector() File "c:\project_ANNIE\project1_module2.py", line 14, in eye_detector gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cv2.error: OpenCV(4.10.0) D:\a\opencv-python\opencv-python\opencv\modules\imgproc\src\color.cpp:196: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

I expected it to turn off the camera and start the next function, but it didn't. The camera wasn't turned off, and the next function didn't work. I need help.

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