Virtual Environments

“A Virtual Environment is a tool to keep the dependencies required by different projects in separate places, by creating virtual Python environments for them. It solves the ‘Project X depends on version 1.x but, Project Y needs 4.x’ dilemma, and keeps your global site-packages directory clean and manageable.”

—Hitchiker’s Guide to Python, Virtual Environments

Virtual environments not only help manage package versions, but also ensure the correct version of the Python intepreter is associated with a project.

• virtualenv is a tool to create these isolated Python environments.
• virualenvwrapper is a set of extensions to Ian Bicking’s virtualenv tool to add the following features:

1. Organize all of your virtual environments in one place.
2. Manage virtual environments (create, delete and list).
3. Allows the use a single command to switch between environments.

• virtualenvwrapper-win is a port of Doug Hellmann’s virtualenvwrapper to Windows

Let’s install virtualenwrapper-win:

pip install virtualenvwrapper-win

Virtual Environment Commands

Command	Description
mkvirtualenv <project-name>	Create a new virtual environment
lsvirtualenv	List all existing virtual environments
setprojectdir <path>	Associate a project folder with a virtual environment
cdproject	Change to the project folder
workon <project-name>	Start up a virtual environment
deactivate	Shown down the virtual environment

Virtualenvwrapper-win Environment Variables

Default Environment Variables (preset by virtualenvwrapper-win):

WORKON_HOME=%USERPROFILE%\Envs
PROJECT_HOME=%USERPROFILE%\.projects

Variable	Description
WORKON_HOME	The directory where the virtual environments will be stored.
PROJECT_HOME	The project directory associated with a virtualenv.

We recommend creating a generic sanbox environment for both Python 2.7 and the latest Python 3 release. The gives you a environment to play, experiment and learn in, but we suggest creating a separate virtual environment for each Python project that you work with.

Here’s how to setup the Python 3.5 sandbox:

C:\> mkvirtualenv cp35
C:\> setprojectdir %PROJECT_HOME%\cp35
C:\> workon cp35

1. This creates new virtual environment we chose to call cp35 (stands for CPython ver. 3.5)
2. This sets the project directory for the virtual environment.
3. This restarts the virtual environment and moves you into the project directory.

Now let’s setup the Python 2.7 sandbox (remember you can use tab completion to avoid typing in the whole name:

C:\> mkvirtualenv -p c:\python\python27\python.exe
C:\> setprojectdir %PROJECT_HOME%\cp27
C:\> workon cp27

Note

Since our default Python Interpreter is 3.5, we need to use the -p option with mkvirtualenv to indicate which interpreter we want to use for the virtual environment.

Summary

When you want to play in CPython 2.7:

C:\> workon cp25

When you want to switch to CPython 3.5:

C:\> workon cp35

When you want to exit the virtual environment:

C:\> deactivate

When you want to create a virtual environment for a new project:

C:\> mkvirtualenv <name>
C:\> setprojectdir <path>
C:\> workon <name>