Tutorial: run ArchGenXML 2.0 under virtualenv

cookbook, Plone

The "modern" (post 1.5) version of ArchGenXML is packaged as egg, available on pypi. While in theory you could run "sudo easy_install archgenxml" and have it running with minimal effort, because it depends on zope.component and zope.configuration, things tend to get muddy and complicated. If you'll "easy_install zope.component" you'll get a bunch of zope eggs installed in python's site-packages and this will probably cause problems. When I've started developing with Zope 3 I had some hard time tracking some problems that ultimately turned out to be caused by zope packages installed in the system python "conflicting" with my regular zope instances. Even the Plone installer prefers to create its own Python directory, to keep the its packages separated from other python packages installed in the system. To solve this problem, ArchGenXML has a mechanism to specify a path to the zope packages, of which I've already blogged about, but I now consider it an extra step which can be avoided by using virtualenv to install the archgenxml egg.

This following recipe is specific to Ubuntu, but probably adaptable to any Linux system, and even Windows. First, if you don't have easy_install in your system, install it with:

#sudo apt-get install python-setuptools
#easy_install virtualenv

In my ~/Software folder I've ran:

#virtualenv agx

This will create a ~/Software/agx virtual environment. We need to activate it:

#source agx/bin/activate

Now all python commands we will run (python, easy_install) will 'belong' to this virtual environment. We can safely install agx, zope.component and zope.configuration, as they will be installed there:

(agx)#easy_install archgenxml
(agx)#easy_install zope.component
(agx)#easy_install zope.configuration

The ArchGenXML egg has defined several console scripts, they're available as scripts "tied" to this virtual python environment, for example, this is the 'archgenxml' script that was installed in my ~/Software/agx/bin folder:

#!/home/tibi/tmp/arch/bin/python2.4
# EASY-INSTALL-ENTRY-SCRIPT: 'archgenxml==2.0-rc1','console_scripts','archgenxml'
__requires__ = 'archgenxml==2.0-rc1'
import sys
from pkg_resources import load_entry_point

sys.exit(
   load_entry_point('archgenxml==2.0-rc1', 'console_scripts', 'archgenxml')()
)

What this tells us is that you can safely run this script from "outside" the virtual environment, without needing to first "source bin/activate" it.