How can I run a function every specific time within a while cycle on python?

debugcn Published at Dev

Alex Ortega

I'm working in a project with OCR using a webcam. I would like to know how can I run a function every 3 seconds (for example) while the principal code still running. The code is very long. So I use the following to exemplify:

import cv2

cap = cv2.VideoCapture(0)

def capture():
    cv2.imwrite("frame.jpg", frame)

while(1):
    ret, frame = cap.read()
    cv2.imshow('Webcam', frame)
    (_, cnt, _) = cv2.findContours(frame, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
    if len(cnt) > 10:
        # here I want to call capture() function every 3 seconds

    if cv2.waitKey(1) & 0xFF == ord('x'):
        break

cap.release()
cv2.destroyAllWindows()

I used time.sleep(3) after the statments of capture() function but it pause the continuous capture of the frame. I don't want it. I need something like a software interruption. When the flag shoots, the code of function run but the while cycle continues working.

I'm using python 2.7 on Windows 7.

I hope you understand my purpose. I rode about daemon and threads but I can't interpret so much.

Joshi Sravan Kumar

You can use it like this

import cv2
import threading
import time

cap=cv2.VideoCapture(0)

main_loop_running = True
def capture():
    global main_loop_running, frame
    while (main_loop_running):
        cv2.imwrite("frame.jpg", frame)
        time.sleep(3)

ret, frame = cap.read()
cv2.imshow('Webcam', frame)
child_t = threading.Thread(target=capture)
child_t.setDaemon(True)
child_t.start()

while(1):
    ret, frame = cap.read()
    cv2.imshow('Webcam', frame)

    # here I want to call capture() function every 3 seconds

    if cv2.waitKey(1) & 0xFF == ord('x'):
        break

main_loop_running = False
child_t.join()

cap.release()
cv2.destroyAllWindows()

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