ERROR issues

[zkzk123zk]

TypeError: unsupported operand type(s) for /: 'NoneType' and 'float'

[JackCobra11]

The same image in different sets has the same name. However, the image format of 'train' is '.jpg', while the others are '.png'. So you need to turn the '.png' files into '.jpg' files. Otherwise, OpenCV can't find you low light images, and return TypeError. (your code can't open your low light datasets image)
Here's the code to modify the file type,

import os

file_path = r"..\train_dark"

files = os.listdir(file_path)

for file in files:

    if file.endswith('png'):

        src = os.path.join(file_path, file)

        r_name = file.split('.')[0] + '.jpg'

        dct = os.path.join(r"..\train_dark", r_name)

        os.rename(src, dct)