Custom waitKey for opencv

main.py

# make sure terminal window is active when pressing any key
import cv2
import numpy as np
import time
from waitKey import waitKey

frame = np.zeros((300, 300, 3))
idx, st = 0, time.time()

while True:
    cv2.imshow("frame", frame)
    
    key = waitKey()
    if key == 's':
        cv2.imwrite("frame.jpg", frame)
    elif key == 'q':
        break

waitKey.py

# https://stackoverflow.com/questions/13207678/whats-the-simplest-way-of-detecting-keyboard-input-in-a-script-from-the-termina
import sys
import select
import termios
import cv2

class waitKey():
    def __init__(self):
        self.fd = sys.stdin.fileno()
        self.new_term = termios.tcgetattr(self.fd)
        self.old_term = termios.tcgetattr(self.fd)

        # New terminal setting unbuffered
        self.new_term[3] = (self.new_term[3] & ~termios.ICANON & ~termios.ECHO)
        termios.tcsetattr(self.fd, termios.TCSAFLUSH, self.new_term)

    def __del__(self):
        termios.tcsetattr(self.fd, termios.TCSAFLUSH, self.old_term)

    def __call__(self):
        cv2.waitKey(1)
        dr,dw,de = select.select([sys.stdin], [], [], 0)
        if not dr == []:
            return sys.stdin.read(1)
        return ''

waitKey = waitKey()