Python Eggs, Generic Setup and Zope 3¶
Background notes on changes between Plone 2.5 and Plone 3.
Products, in Plone's parlance, are analogous to modules or extensions for other applications. In the move from Plone 2.5 to Plone 3, several important changes were made in the way Plone handles products. First, some products began to be packaged as Python eggs, which made them easier to manage, distribute and install. Second, products began to use GenericSetup as a means for installation. And third, products increasingly incorporated Zope 3 (Z3) technologies like browser views.
A python egg is simply a bundle of files and directories which constitute a python package. Eggs can either be compressed, in which case they appear as a single *.egg file, or uncompressed. Eggs are similar in concept and function to Java's JAR files.
Eggs are installed via the setuptools framework, a side project of the Python Enterprise Application Kit (PEAK), which provides for package (and dependendency) management and distribution.
If you're using version control, you'll want to add *.egg-info and *.pyc to the ignore patterns for your setup so that the egg metadata and compiled python files aren't added to your repository.
A good overview of eggs and setuptools from the folks at PEAK.
David Metz takes a look at the setuptools framework.
GenericSetup (GS) is a tool for managing site configuration in Plone using xml files. GS makes it possible to export customizations from one Plone site and import them into another. And to some extent, GS replaces the Portal QuickInstaller (QI) post-Plone 2.5 in that GS can be used to install products. In products which rely on GS, we find xml configuration files; in products which use the older, venerable QI for installation, by comparison, we find install methods written in python.
Keep in mind that GenericSetup does not currently allow you to undo the profile applied during installation. You can uninstall your theme using the QuickInstaller, however, assuming that an uninstall method is present.
Because our skeleton theme product utilizes GenericSetup to install itself, we will shortly be configuring several xml files needed by GS.
Now a bit dated, Rob Miller's tutorial on GS remains a useful resource for background on GS.
More information about GS from Rob Miller.
Impress your colleagues by using GenericSetup and Zope 3 views efficiently and with minimal effort! This tutorial shows you how to add a new view, how to use it, how to add a new content type and how to hook it all up.
Zope 3 Technology¶
Despite any version number-induced miasma, remember that Plone 3 runs on Zope 2. Zope 3 is a dramatic rewrite of Zope 2 and some Zope 3 functionality has been backported to work under Zope 2. (And yes, Plone 3.) For a full explanation of the Zope 3 technologies involved, consult this tutorial:
An overview of Plone 3 customization by Martin Aspeli.