Using Virtualenv for a clean Grok installation¶

Author:	unknow

NOTE: As of Grok 1.2, you do not need to use virtualenv. Grok is automatically isolated from the system python environment.

Benefits of Using Virtualenv¶

Virtualenv is a python tool that allows you to create isolated python environments. It is great for simplifying the environment for your Grok installation so that you don’t run into version or permissions problems. It can also be used as a solution for installing python packages on machines where you do not have write access to the site-packages directory.

It’s really easy to use virtualenv
Virtualenv can allow you to have different Zope versions on your system (or any conflicting python software). This can be very useful if you run Plone and Grok on the same machine, or if you use a stand alone Zope version that is different from the Zope version that Grok uses.
Virtualenv will allow you to install Grok on a system to which you do not have write access to the system wide python directory.

Example of conflicting packages¶

You have already installed Zope 3.1 for a previous development task. This was installed system wide and has placed a number of packages in your site-packges directory. Grok currently requires the Zope Toolkit (ZTK). Running grokproject produces an error and aborts it’s process.

Virtualenv provides a fix by allowing you to use your Python installation without the packages installed in the default site-packages directory.

What you need¶

A working Python installation with virtualenv and easy_install is required.

You can install virtualenv with easy_install:

$ easy_install virtualenv

If you have newer versions of Python on your system, then you can target the required version of easy_install with:

easy_install-2.6 virtualenv

Debian specific instructions¶

If you are using a Debian-based system, you can use the apt package management tool to install virtualenv. For Debian this is available on the unstable branch (Sid) as python-virtualenv:

# apt-get install python-virtualenv

The current stable release of Debian 4.0 (Etch) does not have the python-virtualenv package available, but does have easy_install available, so you can install it by running:

# apt-get install python-setuptools
# easy_install virtualenv

Creating a new Python sandbox¶

Create the virtual python environment¶

Run the virtualenv command to create a new, clean Python environment by the name of ‘virtualgrok’:

virtualenv --no-site-packages virtualgrok

This creates a directory called ‘virtualgrok’ with two folders within it, lib and bin. This will look like this:

NOTE: Grok 1.1 requires python 2.6 or 2.5 (2.4 deprecated) so you would have easy_install-2.5/-2.6 and python2.5/2.6.

The optional –no-site-packages switch means that none of your existing Python site-packages will be available in your new Python environment. This is desirable if you already have conflicting Python packages installed that you want to avoid (or might install such packages in the future).

Some Zope developers do not use this switch as they have installed a second Python (or sometimes many more!) separate from the system Python for developing Python web applications with. They only install the more difficult to install packages into their development Python such as PIL, XML, database and LDAP packages available and then use a separate virtual environment for each major Zope project they work on. Zope developer Lennart Regebro has termed this approach as “having both a belt and suspenders”.

Activate your virtual python environment¶

VirtualEnv creates a shell file called activate which you can optionally use to alter your PATH environment variable so that you do not have to type the full path to your new Python (e.g. /home/username/virtualgrok/bin/python). Let’s look at how you can use the source shell command with this activate file to make the new python the default:

$ echo $PATH
usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin
$ which python
/usr/bin/python
$ source virtualgrok/bin/activate
(virtualgrok)$ echo $PATH
/home/username/virtualgrok/bin:usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin
(virtualgrok)$ which python
/home/username/virtualgrok/bin/python
(virtualgrok)$ deactivate
$