15. Write Your Own Add-Ons to Customize Plone

In this part you will:

  • Create a custom Python package ploneconf.site to hold all the code
  • Modify buildout to install that package

Topics covered:

  • mr.bob and bobtemplates.plone
  • the structure of eggs

Creating the package

Our own code has to be organized as a Python package, also called egg. An egg is a zip file or a directory that follows certain conventions. We are going to use bobtemplates.plone to create a skeleton project. We only need to fill in the blanks.

We create and enter the src directory (src is short for sources) and call a script called mrbob from our buildout’s bin directory:

$ mkdir src      # (if src does not exist already)
$ cd src
$ ../bin/mrbob -O ploneconf.site bobtemplates:plone_addon

We have to answer some questions about the add-on. We will press Enter (i.e. choosing the default value) for all questions except 3 (where you enter your github username if you have one) and 5 (Plone version), where we enter 5.0.6:

--> What kind of package would you like to create? Choose between 'Basic', 'Dexterity', and 'Theme'. [Basic]:

--> Author's name [Philip Bauer]:

--> Author's email [bauer@starzel.de]:

--> Author's github username: fulv

--> Package description [An add-on for Plone]:

--> Plone version [5.0.5]: 5.0.6

Generated file structure at /vagrant/buildout/src/ploneconf.site

If this is your first egg, this is a very special moment. We are going to create the egg with a script that generates a lot of necessary files. They all are necessary, but sometimes in a subtle way. It takes a while to understand their full meaning. Only last year I learned and understood why I should have a MANIFEST.in file. You can get along without one, but trust me, you get along better with a proper manifest file.

Inspecting the package

In src there is now a new folder ploneconf.site and in there is the new package. Let’s have a look at some of the files:

bootstrap-buildout.py, buildout.cfg, travis.cfg, .travis.yml, .coveragerc
You can ignore these files for now. They are here to create a buildout only for this egg to make testing it easier. Once we start writing tests for this package we will have another look at them.
The documentation, changelog, the list of contributors and the license of your egg goes in here.
This file configures the package, its name, dependencies and some metadata like the author’s name and email address. The dependencies listed here are automatically downloaded when running buildout.
The package itself lives inside a special folder structure. That seems confusing but is necessary for good testability. Our package contains a namespace package called ploneconf.site and because of this there is a folder ploneconf with a __init__.py and in there another folder site and in there finally is our code. From the buildout’s perspective our code is in your buildout directory/src/ploneconf.site/src/ploneconf/site/real code


Unless discussing the buildout we will from now on silently omit these folders when describing files and assume that your buildout directory/src/ploneconf.site/src/ploneconf/site/ is the root of our package!

configure.zcml (src/ploneconf/site/configure.zcml)
The phone book of the distribution. By reading it you can find out which functionality is registered using the component architecture.
setuphandlers.py (src/ploneconf/site/setuphandlers.py)
This holds code that is automatically run when installing and uninstalling our add-on.
interfaces.py (src/ploneconf/site/interfaces.py)
Here a browserlayer is defined in a straightforward python class. We will need it later.
This holds the setup for running tests.
This holds the tests.
This directory is a python package (because it has a __init__.py) and will by convention hold most things that are visible in the browser.
The phonebook of the browser package. Here views, resources and overrides are registered.
This add-on is already configured to allow overriding existing default Plone templates.
A directory that holds static resources (images/css/js). The files in here will be accessible through URLs like ++resource++ploneconf.site/myawesome.css
This folder contains the GenericSetup profile. During the training we will put some XML files here that hold configuration for the site.
Version number and dependencies that are auto-installed when installing our add-on.

Including the package in Plone

Before we can use our new package we have to tell Plone about it. Look at buildout.cfg and see how ploneconf.site is included in auto-checkout, eggs and test:

auto-checkout +=
#    starzel.votable_behavior

parts =

eggs =

# development tools

# TTW Forms (based on Archetypes)

# The add-on we develop in the training

# Voting on content
#    starzel.votable_behavior

zcml =

test-eggs +=
    ploneconf.site [test]

This tells Buildout to add the egg ploneconf.site. The sources for this eggs are defined in the section [sources] at the bottom of buildout.cfg.

ploneconf.site = git https://github.com/collective/ploneconf.site.git pushurl=git@github.com:collective/ploneconf.site.git
starzel.votable_behavior = git https://github.com/collective/starzel.votable_behavior.git pushurl=git://github.com/collective/starzel.votable_behavior.git

The tells buildout not to download it from pypi but to do a cjeckout from github put the code in src/ploneconf.site.


The package ploneconf.site is now downloaded from github and automatically in the branch master


If you do not want to use the prepared package for ploneconf.site from github but write it yourself (we suggest you try that) then add the following instead:

ploneconf.site = fs ploneconf.site path=src
starzel.votable_behavior = git https://github.com/collective/starzel.votable_behavior.git pushurl=git://github.com/collective/starzel.votable_behavior.git

This tells buildout to expect ploneconf.site in src/ploneconf.site. The directive fs allows you to add eggs on the filesystem without a version control system.

Now run buildout to reconfigure Plone with the updated configuration:

$ ./bin/buildout

After restarting Plone with ./bin/instance fg the new add-on ploneconf.site is available for install like PloneFormGen or Plone True Gallery.

We will not install it now since we did not add any of our own code or configuration yet. Let’s do that next.