It&#x27;s for both libraries and different versions of Python. This is common and trivial.
I install specific versions of Python using the Deadsnakes PPA since I can easily pull in any version going back to 2.3 if I need. Or you can compile and install from source.<p>Then create a folder for your project, &#x27;virtualenv -p &#x2F;usr&#x2F;bin&#x2F;python3.5 venv&#x27; to create the venv in that directory.
Activate&#x2F;deactivate the environment as you wish when you want go between the system Python environment and the one in your folder.