= MBTilesBuilder(filepath='output.mbtiles', tiles_url='http://tile.stamen.com/watercolor/{z}/{x}/ {y}.jpg')
mb.add_coverage(bbox=(-122.1099,37.4531,-121.8768,37.6107), zoomlevels=range(12, 16))
mb.run() If no URL given, it’ll just grab from the official OpenStreetMaps server.
Guarantee ugly tiles (sorry, OSM), but easy peasy. Python script to get images from server