[galaxy-dev] Trying to understand python dependencies

I have galaxy server 15.10 running on Ubuntu 14.04, which has python 2.7.5. I was in the process of adding matplotlib from the toolchest. It has a dependency on package_python_2_7. Before proceeding, I'd like to understand a bit how that works. Does that install a whole new python, and how then does it get invoked? Tony Schreiner