For example, to find the lat/lng bounding box of the top-most tile in the standard Google map, which is tile (0,0) at zoom-level 0, you would do:
> python >> import mercator >> mercator.get_tile_box(0, 0, 0) (-85.05112877980659, 85.05112877980659, -180.0, 180.0)
So, the entire Google map has the full range of longitudes, but only goes to +/-85.05 degrees latitude, which is to be expected since the Mercator projection maps +/-90 degrees latitude to +/-infinity.
then you'll see the coordinate of the top-left part of the map, which again is:
Back in Python, we can see what tile (0, 0) at zoom-level 1 looks like:
>> mercator.get_tile_box(1, 0, 0) (0.0, 85.05112877980659, -180.0, 0.0)
As we would hope, it is the top-left quadrant of the map, since at zoom=1 there are (2^zoom * 2^zoom) == 4 tiles.