This is a Heroku buildpack that allows you to install swig which is a system dependency needed for many libraries to function correctly. E.g. M2Crypto.
To use this buildpack you'll first need to set the multi buildpack as your custom buildpack:
$ heroku buildpacks:set https://github.com/heroku/heroku-buildpack-multi.git
From here you will need to create a
.buildpacks file which contains this buildpack and then the other buildpacks which will trigger dependencies on swig.
$ cat .buildpacks https://github.com/jamarparris/heroku-buildpack-swig https://github.com/heroku/heroku-buildpack-python
Copy the snippet above into CLI.