You can use TileDownloader project for dowloading tiles from any online map server or custom location. But it is writed in Visual Basic and contains hardcoded file extension for tiles :(
#Merge tiles
For merging map tiles into one file you may run mergetiles.py script with several parameters:
python mergetiles.py -i <input directiry> -o <output file>
For example:
python mergetiles.py -i "C:/demo/" -o "C:/demo/result.jpg"
After start, script will find first file in firts direcory and try to get width of image. Size of all tiles mush be equal.
Next it will find tiles by mask baseDir/<y>/<x>.<tileExtension>, there y is row number and x is column number, and merge them into one image.