PYTHONPATH is an environment variable- Yes (see https://unix.stackexchange.com/questions/24802/on-which-unix-distributions-is-python-installed-as-part-of-the-default-install)
/usr/lib/python2.7 on Ubuntu- you shouldn't install packages manually. Instead, use pip. When a package isn't in pip, it usually has a setuptools setup script which will install the package into the proper location (see point 3).
- if you use pip or setuptools, then you don't need to set
PYTHONPATH explicitly
If you look at the instructions for pyopengl, you'll see that they are consistent with points 4 and 5.
