How to loop with R string Python

Currently, my code is like this:

for images in range(500):
    image = cv2.imread(r'C:\\mypath\images.png')

How can I loop through? I tried using {}.format(images) but that doesn’t work with r strings?

edit: updated code problem

for i in range(500):
    image = cv2.imread(fr'mypath\captcha{i}.png')
    img_gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    ret, thresh = cv2.threshold(img_gray, 150, 255, cv2.THRESH_BINARY)
    cv2.imshow('Binary image', thresh)
    cv2.imwrite(fr'mypath\captcha{i}.png', thresh)

error:

cv2.error: OpenCV(4.5.4) D:\a\opencv-python\opencv-python\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

>Solution :

Why not just use f-strings ?

for images in range(500):
    image = cv2.imread(f'C:\\mypath\{images}.png')

If r-strings needed, then just use fr-strings, e.g.:

for images in range(500):
    image = cv2.imread(fr'C:\\mypath\{images}.png')

Maybe you need to change \ to / as well. Sometimes it’s necessary.