For Debian based GNU/Linux
A lot of built in programs in Linux, OSX or POSIX compilant often rely on the system python, the executable to which, is in /usr/bin/python. Because a lot depend on it, it is not a good idea to mess with it, change it's version, or add new libraries into it.
The better way is to have the dependencies contained within it's own environment, so system python changes (due to upgrade) and other environment's changes don't affect the current project.
the steps below mostly compatible with Debian based GNU/Linux. however, it may possible on OSX and other linux distributions too. The main idea is just the same.