heroku/heroku-buildpack-python — pull request #184 by kainz (2014-11-20 01:52:29+00:00)
Title: Add support for working in conjuction with other buildpacks.

If you are using heroku-buildpack-multi and/or heroku-buildpack-apt with
heroku-buildpack-python, you probably want to be smart about prepending
your paths, and also accept the build environment's LD_LIBRARY_PATH and
LIBRARY_PATH.

The ${STUFF:+} alternative expansion used here is to avoid adding
extraneous : characters to these path variables.