Python Virtual Environment

Virtual Python Environment builder
==================================

`virtualenv` is a tool to create isolated Python environments.

Virtualenv is probably what you want to use during development, and in
production too if you have shell access there.

What problem does Virtualenv solve? If you like Python as I do, chances are
you want to use it for other projects besides [Werkzeug-based web applications](http://werkzeug.pocoo.org).
But the more projects you have, the more likely it is that you will be working
with different versions of Python itself, or at least different versions of
Python libraries. Let's face it; quite often libraries break backwards
compatibility, and it's unlikely that any serious application will have zero
dependencies. So what do you do if two or more of your projects have
conflicting dependencies?

Virtualenv to the rescue! It basically enables multiple side-by-side
installations of Python, one for each project. It doesn't actually install
separate copies of Python, but it does provide a clever way to keep different
project environments isolated.

So let's see how virtualenv works!

If you are on *Mac OSX* or *Linux*, chances are that one of the following two
commands will work for you:

    $ sudo easy_install virtualenv

or even better:

    $ sudo pip install virtualenv

One of these will probably install virtualenv on your system. Maybe it's even
in your package manager. If you use Ubuntu, try:

    $ sudo apt-get install python-virtualenv

If you are on Windows and don't have the `easy_install` command, you must
install it first. Once you have it installed, run the same commands as above,
but without the `sudo` prefix.

Once you have virtualenv installed, just fire up a shell and create your own
environment. I usually create a project folder and an env folder within:

    $ mkdir myproject
    $ cd myproject
    $ virtualenv env
    New python executable in env/bin/python
    Installing setuptools............done.

Now, whenever you want to work on a project, you only have to activate the
corresponding environment. On OS X and Linux, do the following:

    $ . env/bin/activate

> **Note** the space between the dot and the script name. The dot means that
> this script should run in the context of the current shell. If this
> command does not work in your shell, try replacing the `.` with `source`.

If you are a Windows user, the following command is for you:

    $ env\scripts\activate

Either way, you should now be using your virtualenv (see how the prompt of
your shell has changed to show the virtualenv).

Now you can just enter the following command to get Werkzeug activated in your
virtualenv:

A few seconds later you are good to go.

---

**Source**

- [_Werkzeug_](http://werkzeug.pocoo.org/docs/installation/#virtualenv) Installation Guide

**Additional Resources**

- [Virtualenv Python Package Index](https://pypi.python.org/pypi/virtualenv)