import os
import pathlib
import glob, os
from pathlib import Path
import os.path
from os import path
import mmap

jpg_index = "jpgfilestorage.txt"

search_locations = ["C:\\path\\to\\foldera", "C:\\path\\to\\folderb"]

if os.path.exists(jpg_index):
    for search_location in search_locations:
        for path in Path(search_location).rglob('*.jpg'):
            with open(jpg_index) as file, \
                mmap.mmap(file.fileno(), 0, access=mmap.ACCESS_READ) as s:
                if s.find(str.encode(path.__str__())) < 0:
                    with open(jpg_index, 'a') as filehandle:
                        filehandle.writelines('%s\n' % path)