If you are working on many projects simultaneously, or even just switching between them frequently, you'll find that having everything installed system-wide is not the best option and can bring problems in future on different systems (production) where you want to run your software. This is not a good time to find out that you are missing a certain package or have versioning conflicts between packages that are already installed on production system; hence, virtualenv.
virtualenv is an open source project started by Ian Bicking that enables a developer to isolate working environments per project, for easier maintenance of different package versions.
For example, you inherited legacy Django website based on Django 1.1 and Python 2.3, but at the same time you are working on a new project that must be written in Python 2.6. This is my usual case—having more than one required Python version (and related packages) depending on the project I am working on.
virtualenv enables me to easily switch to different environments and have the same package easily reproduced if I need to switch to another machine or to deploy software to a production server (or to a client's workstation).
To install virtualenv, you must have workable installation of Python and pip. Pip is a tool for installing and managing Python packages, and it is a replacement for easy install. We will use pip through most of this book for package management. Pip is easily installed, as root executes the following line in your terminal:
# easy_install pip
virtualenv by itself is really useful, but with the help of virtualenvwrapper, all this becomes easy to do and also easy to organize many virtual environments. See all the features at http://virtualenvwrapper.readthedocs.org/en/latest/#features.
By performing the following steps you can install the virtualenv and virtualenvwrapper tools:
Install virtualenv and virtualenvwrapper:
$ sudo pip virtualenv $ sudo pip virtualenvwrapper # Create folder to hold all our virtual environments and export the path to it. $ export VIRTENV=~/.virtualenvs $ mkdir -p $VIRTENV # We source (ie. execute) shell script to activate the wrappers $ source /usr/local/bin/virtualenvwrapper.sh # And create our first virtual environment $ mkvirtualenv virt1
You can now install our favorite package inside
virt1:(virt1)user1:~$ pip install matplotlibYou will probably want to add the following line to your
~/.bashrcfile:source /usr/loca/bin/virtualenvwrapper.sh
Few useful and most frequently used commands are as follows: