Virtual Environments

A Virtual Environment, put simply, is an isolated working copy of Python which allows you to work on a specific project without worry of affecting other projects.

For example, you can work on a project which requires Django 1.3 while also maintaining a project which requires Django 1.0.

virtualenv

virtualenv is a tool to create isolated Python environments.

Install it via pip:

$ pip install virtualenv

Basic Usage

  1. Create a virtual environment:
$ virtualenv venv

This creates a copy of Python in whichever directory you ran the command in, placing it in a folder named venv.

  1. To begin using the virtual environment, it needs to be activated:
$ source venv/bin/activate

You can then begin installing any new modules without affecting the system default Python or other virtual environments.

  1. If you are done working in the virtual environment for the moment, you can deactivate it:
$ deactivate

This puts you back to the system’s default Python interpreter with all its installed libraries.

To delete a virtual environment, just delete its folder.

After a while, though, you might end up with a lot of virtual environments littered across your system, and its possible you’ll forget their names or where they were placed.

virtualenvwrapper

virtualenvwrapper provides a set of commands which makes working with virtual environments much more pleasant. It also places all your virtual environments in one place.

To install (make sure virtualenv is already installed):

$ pip install virtualenvwrapper
$ export WORKON_HOME=~/Envs
$ source /usr/local/bin/virtualenvwrapper.sh

(Full virtualenvwrapper install instructions.)

For Windows, you can use the virtualenvwrapper-powershell clone.

To install (make sure virtualenv is already installed):

PS> pip install virtualenvwrapper-powershell
PS> $env:WORKON_HOME="~/Envs"
PS> mkdir $env:WORKON_HOME
PS> import-module virtualenvwrapper

Basic Usage

  1. Create a virtual environment:
$ mkvirtualenv venv

This creates the venv folder inside ~/Envs.

  1. Work on a virtual environment:
$ workon venv

virtualenvwrapper provides tab-completion on environment names. It really helps when you have a lot of environments and have trouble remembering their names.

workon also deactivates whatever environment you are currently in, so you can quickly switch between environments.

  1. Deactivating is still the same:
$ deactivate
  1. To delete:
$ rmvirtualenv venv

Other useful commands

lsvirtualenv
List all of the environments.
cdvirtualenv
Navigate into the directory of the currently activated virtual environment, so you can browse its site-packages, for example.
cdsitepackages
Like the above, but directly into site-packages directory.
lssitepackages
Shows contents of site-packages directory.

Full list of virtualenvwrapper commands.

autoenv

When you cd into a directory containing a .env, autoenv automagically activates the environment.

Install it on Mac OS X using brew:

$ brew install autoenv

And on Linux:

$ git clone git://github.com/kennethreitz/autoenv.git ~/.autoenv
$ echo 'source ~/.autoenv/activate.sh' >> ~/.bashrc

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This opinionated guide exists to provide both novice and expert Python developers a best-practice handbook to the installation, configuration, and usage of Python on a daily basis.

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