Take screenshot of specific window on MacOS with python

take-screenshot-mac.py

from Quartz import CGWindowListCopyWindowInfo, kCGNullWindowID, kCGWindowListOptionAll
import cv2 as cv
import numpy
from time import time
from PIL import Image
import os

windowId = None
windowName = 'Desktop'


def findWindowId():
    global windowId

    print('searching window id')

    windowList = CGWindowListCopyWindowInfo(
        kCGWindowListOptionAll, kCGNullWindowID)

    for window in windowList:
        print(window.get('kCGWindowName', ''))
        if(windowName.lower() in window.get('kCGWindowName', '').lower()):
            windowId = window['kCGWindowNumber']
            print('found window id %s' % windowId)
            return True

    print('unable to find window id')
    return False


def takeScreenshot():
    if windowId is None:
        if findWindowId() is False:
            return

    imageFileName = 'test-img.png'
    # -x mutes sound and -l specifies windowId
    os.system('screencapture -x -l %s %s' % (windowId, imageFileName))
    img = Image.open(imageFileName)
    print(img)
    img = numpy.array(img)
    os.remove(imageFileName)
    return img


loopTime = time()

while(True):
    screenshot = takeScreenshot()

    if screenshot is not None:
        cv.imshow('cv', screenshot)

    # measure frames per second
    print('FPS {}'.format(1 / (time() - loopTime)))
    loopTime = time()

    if cv.waitKey(1) == ord('q'):  # quit script when pressing 'q' key
        cv.destroyAllWindows()
        break


print('Done.')

This helped me tremendously - thank you so much!

fp = builtins.open(filename, "rb")

FileNotFoundError: [Errno 2] No such file or directory: 'test-img.png' - - why？