Virtual environment

A virtual environment is a “space” separated from operating system, where Python packages get installed. This “space” is local, thus prevents Python packages from overwriting your system Python packages.

Imagine having package xyz in version 1.2.4 installed system-wide. Now you want to install Ganeti Web Manager, that requires this package in version 1.1.

You can’t keep both packages installed system-wide. Therefore you need to somehow separate packages required by Ganeti Web Manager and your system packages. Virtual environment does exactly this.

Virtual environment structure

Virtual environment (shortly virtualenv or venv) consists of these directories:

  • bin - contains executable files and activation scripts
  • include - contains symlink to lib/python2.x directory
  • lib - Python packages get installed to this directory
  • local - contains symlinks to bin, include and lib directories
  • share - contains documents and man pages installed along with Python packages

Helpers and tools

Main tool used for creating virtual environments is python-virtualenv and it’s executable: virtualenv.

When you issue virtualenv name in your shell, this tool creates structure described above in the name directory.

Usually next thing to do when developing (or deploying) a project in Python is to clone a repository within that virtual environment. It creates your project files next to virtual environment‘s directories. And everything becomes a mess.

To help overcome this mess, someone clever wrote virtualenvwrapper. This is a set of shell scripts, that:

  • create virtual environment in your $HOME/.virtualenvs directory
  • list virtual environments existing there
  • remove specified virtual environment
  • quickly switch between existing virtual environments

...and we highly recommend using it.

virtualenvwrapper commands

mkvirtualenv name
Creates virtual environment with given name.
List all existing virtual environments.
rmvirtualenv name
Remove existing virtual environment with given name.
workon name
Switch to virtual environment with given name.
When you’re within virtual environment, you can leave it by issuing this command.

Command line prompt

By default, after activating specific virtual environment, it’s name appears at the beginning of your shell prompt. For example:

$ cd ganeti_webmgr
$ workon gwm
(gwm)$ --help
(gwm)$ deactivate
$ lsvirtualenv


In some guides in this documentation these brackets indicate commands issued from within virtual environment.