First, set DATABASE_FILE in app.cfg to be the path to your census-data.db file. If you have Flask installed, you can then run python app.py to start the server; it will start on localhost:5000 by default. The code should work well with any sqlite file as long as the VARIABLE parameter is set to a column that actually exists and is numeric.
The first 16000 lines of census-data.db appear to have null values for every column. I decided to just filter them out when I return the results. Depending on the use case, a better option could be to clean the table only once before using it with this script.