Virtualenv and pip

In this section you will:

  • use pip to install packages
  • install virtualenv
  • create and destroy, activate and deactivate virtual environments
  • use pip freeze to show installed items

What is virtualenv?

Virtualenv lets you create and manage virtual Python environments.

If you’re running a Python project for deployment or development, the chances are that you’ll need more than one version of it, or the numerous other Python applications it depends upon, at any one time.

For example, when a new version of Django is released, you might want to check to see if your project is still compatible. You don’t want to have to set up a whole new server with a different version of Django to find out.

With virtualenv, you can quickly set up a brand new Python environment, and install your components into it - along with the new version of Django, without touching or affecting what you already have running.

You can have literally dozens of virtualenvs on the same machine, all running different versions of your Python software, all independently of each other, and can safely make changes to one without affecting anything else.

pip goes hand-in-hand with virtualenv; in fact, it comes with virtualenv (as well as separately). It’s an installer, and is the easiest way to install things into a virtualenv.

Installing pip

You will most probably find that pip is already installed on your system.


pip --version

to find out.

If it’s not, you have various options.

On Debian/Ubuntu systems

sudo apt-get install python-pip

On Debian you probably will not be authorised to use sudo. In this case use:

su -

to switch to the root user before installing pip.


Another option is to use the official script.

Install virtualenv


virtualenv --version

Keep it up-to-date:

sudo pip install --upgrade virtualenv
hash -r # purge shell's PATH, though this may not be necessary for you

If you got a “Command not found” when you tried to use virtualenv, try:

sudo pip install virtualenv


sudo apt-get install python-virtualenv # for a Debian-based system

If that fails or you’re using a different system, you might need more help:

Create and activate a virtual environment

virtualenv my-first-virtualenv
cd my-first-virtualenv
source bin/activate


Windows users should run Scripts\activate instead of source bin/activate.

Notice how your command prompt tells you that the virtualenv is active (and it remains active even while you’re not in its directory):


Using pip

pip freeze

pip freeze lists installed Python packages:

(my-first-virtualenv)daniele@v029:~/my-first-virtualenv$ pip freeze

pip install

Earlier, you may have used sudo pip install. You don’t need sudo now, because you’re in a virtualenv. Let’s install something.

pip install rsa

pip will visit PyPI, the Python Package Index, and will install Python-RSA (a “Pure-Python RSA implementation”). It will also install its dependencies - things it needs - if any have been listed at PyPI.

Now see what pip freeze reports. You will probably find that as well as Python-RSA it installed some other packages - they were ones that Python-RSA needed.

And try:

(my-first-virtualenv)~/my-first-virtualenv$ python
Python 2.7.2+ (default, Jul 20 2012, 22:15:08)
[GCC 4.6.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import rsa

To uninstall it:

pip uninstall rsa

To install a particular version:

pip install rsa==3.0

To ugrade the package to the latest version:

pip install --upgrade rsa

Where packages get installed

Your virtualenv has a site-packages directory, in the same way your system does. So now rsa can be found in:


(It’s possible that you’ll have a different version of Python listed in that path.)


Python-RSA doesn’t have any dependencies, but if it did, and if those dependencies had dependencies, pip would install them all.

So if all the package authors have done a good job of informing PyPI about their software’s requirements, you can install a Django application, for example, and pip will will install it, and Django, and possibly dozens of other pieces of software, all into your virtualenv, and without your having to make sure that everything required is in place.

Managing virtualenvs

Create a second virtualenv

cd ~/ # let's not create it inside the other...
virtualenv my-second-virtualenv

When you activate your new virtualenv, it will deactivate the first:

cd my-second-virtualenv
source bin/activate


Windows users: don’t forget to use Scripts\activate rather than source bin/activate.

pip freeze will show you that you don’t have Python-RSA installed in this one - it’s a completely different Python environment from the other, and both are isolated from the system-wide Python setup.

Deactivate a virtualenv manually

Activating a virtualenv automatically deactivates one that was previously active, but you can also do this manually:


Now you’re no longer in any virtualenv.


When you create a virtualenv, it doesn’t include any Python packages already installed on your system. But sometimes you do want to install all packages. In that case you’d do:

virtualenv --system-site-packages my-third-virtualenv

remove a virtualenv

virtualenvs are disposable. You can get rid of these:

cd ~/
rm -r  my-first-virtualenv my-second-virtualenv my-third-virtualenv

And that’s pretty much all you need to get started and to use pip and virtualenv effectively.