Appendix: dealing with virtualenvs

When dealing with python packages, it is possible to install them as root and make them available for the entire system. This is not always recommended as it can sometimes cause conflicts with the packages installed by your OS.

In the python world a solution to deal with that problem has emerged and allows to create sandboxes in which to install python packages, so that they do not interfere with those of the system. These sandboxes are called virtualenvs, short for “virtual environments”.

Although very powerful, the usage of the bare virtualenv functionality can sometimes be cumbersome, so it is very recommended to use another project instead that gives you an easier API to work with: virtualenvwrapper

The main commands that virtualenvwrapper provides are the following:

  • mkvirtualenv creates a new virtualenv (rmvirtualenv deletes it)
  • workon allows to “activate” a virtualenv, meaning all packages that you install after that will be installed inside this virtualenv, and they will take precedence over those of the system (basically, they will be active). (use deactivate to stop using it)

Example

If you want to create a new virtualenv with python3 being used as interpreter of choice, you would run the following:

$ mkvirtualenv -p `which python3` bts_tools

Note that after creating it, the virtualenv is already active, so you don’t need to call workon bts_tools right after creating it. You will have to do it next time you reboot or open a shell, though.

If you then run the following:

$ pip install bts_tools

it will install the tools inside the virtualenv, and won’t interfere with your system.