How to correctly find contours?

Hi I wrote this code with the objective of detect contours of an object from a live video produced by a camera (in videoCapture I put 0 as input to indicate the camera built-in of computer.

import cv2
import numpy as np

def nothing(x):
    pass

cap = cv2.VideoCapture(0)

cv2.namedWindow("Trackbars")
cv2.createTrackbar("L-H", "Trackbars", 0, 180, nothing)
cv2.createTrackbar("L-S", "Trackbars", 68, 255, nothing)
cv2.createTrackbar("L-V", "Trackbars", 154, 255, nothing)
cv2.createTrackbar("U-H", "Trackbars", 180, 180, nothing)
cv2.createTrackbar("U-S", "Trackbars", 255, 255, nothing)
cv2.createTrackbar("U-V", "Trackbars", 243, 255, nothing)


while True:
_, frame = cap.read()

   hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

   l_h = cv2.getTrackbarPos("L-H", "Trackbars")
   l_s = cv2.getTrackbarPos("L-S", "Trackbars")
   l_v = cv2.getTrackbarPos("L-V", "Trackbars")
   u_h = cv2.getTrackbarPos("U-H", "Trackbars")
   u_s = cv2.getTrackbarPos("U-S", "Trackbars")
   u_v = cv2.getTrackbarPos("U-V", "Trackbars")

   lower_red = np.array([l_h, l_s, l_v])
   upper_red = np.array([u_h, u_s, u_v])

   mask = cv2.inRange(hsv, lower_red, upper_red)

   # rilevazione contorni

   _, contours, _ = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
   print(contours)
   for cnt in contours:
      cv2.drawContours(frame, [int(cnt)], 0, (0, 0, 0), 5)

   cv2.imshow("Frame", frame)
   cv2.imshow("Mask", mask)

   key = cv2.waitKey(1)
   if key == 27:
      break

cap.release()
cv2.destroyAllWindows()

when the execution arrives to cv2.findContours I receive this error message

Traceback (most recent call last):
  File "c:\Users\gpoli\Desktop (3176)\peachthon\rilevaContorno.py", line 37, in <module>
    _, contours, _ = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)     
ValueError: not enough values to unpack (expected 3, got 2)

>Solution :

findContours has two parameters as output not three- In new version of OpenCV.

contours, hierarchy = cv.findContours(thresh, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

What are contours?

OpenCV (findContours) Detailed Guide