Example Scenario

1. Larry lives with Curly and Moe.

2. Larry gets the utility bill, and enters it as an expenditure on their BlueChips site. Everyone shares the utilities, so it’s just an even split.

3. A week later, Moe pays the rent. Curly has a smaller room, so he pays a smaller fraction of the rent.

4. At any time, any user can visit the BlueChips site and see who needs to pay who how much in order to settle the books.

5. After a few months, Moe has paid for a disproportionate amount of stuff, so the other roommates each make a transfer to Moe, and enter the amounts in BlueChips.

Additional Features

• Support for negative expenses

• Uses any authentication mechanism which can set the REMOTE_USER environment variable, including authentication modules supported by Apache, nginx, lighttpd, and others.

• Email notifications of changes (optional)

• 100% test coverage

Installation and Setup

Install BlueChips using easy_install:

easy_install BlueChips

Make a config file as follows:

paster make-config BlueChips config.ini

Tweak the config file as appropriate and then setup the application:

paster setup-app config.ini

Host the application behind an authentication layer which sets REMOTE_USER.

Apache Configuration

The recommended deployment platform for BlueChips is Apache, mod_wsgi, and any Apache module which provides authentication. Here is an example vhost configuration:

<VirtualHost bluechips.example.com:80>
    ServerName bluechips.example.com

    WSGIScriptAlias / /var/www/bluechips.wsgi
    <Directory /var/www>
        Order deny,allow
        Allow from all
    </Directory>

    <Location />
        AuthType Basic
        AuthName "Example BlueChips Site"
        AuthUserFile /etc/apache2/passwords
        Require valid-user
    </Location>
</VirtualHost>

The bluechips.wsgi wrapper script looks just like:

from paste.deploy import loadapp
application = loadapp('config:/var/www/ssl/config.ini')

Acknowledgments

BlueChips is the latest in a long line of software to make managing group finances easier, and would not be possible without the intellectual inspiration of those predecessors.

CUTCAT’s accounting software started the trend of software-based accounting mechanisms. It inspired a re-implementation as a curses script by Nelson Elhage, which introduced the notion of “pushing expenditures” to simplify transfers. The algorithm used in BlueChips for settling the books is directly cargo-culted from Nelson’s implementation.