An extendable Pyramid application using PCA and Jinja2 plugins

Pyramid is a great framework for developing web applications that also supports the development of "Extensible" and "Pluggable" software based on certain rules. However, there is no much documentation on how to create such type of applications.

CKAN is an excellent example of a Web application that can be extended or customized using plug-ins. It relies on PyUtilib Component Architecture to declare a series of interfaces and extension points that then are used by plug-ins to hook in. It also implements a series of Jinja2 extension (notably CKAN_EXTENDS) that allows easily template inheritance between CKAN and connected plug-ins.

CKAN however was developed using Pylons which is now superseded by Pyramid and coupled to its complexity makes it difficult to grasp how to apply such extensibility to Pyramid web applications.

This example applies a modified version of CKAN extensible system to a simple Pyramid application that can be used as a starting point to develop more complex extendable web applications. The example allows plug-ins to extend the host by:

• Adding new routes
• Adding and overwriting templates
• Adding new static resources
• Adding new JSS or CSS resources
• Easy Jinja2 template inheritance and resource injection

The example (pcaexample) is based on a “pyramid-cookiecutter-alchemy” Cookiecutter while the plug-in is based on a “pyramid-cookiecutter-starter”. Both use Python 3.

Please note that this example implements Pyramid "Extensible" and "Pluggable" capabilities in a way that I feel it would satisfy most needs. I don't claim is the best nor the most logical way of doing it. See FormShare for a real example of this approach.

Comments and suggestions are welcomed.

Installation and testing

To build and run the example host application (pcaexample) on Linux do:

git clone https://github.com/qlands/pyramid-pca-jinja2.git
python3 -m venv pcaexample_env
source ./pcaexample_env/bin/activate
cd pyramid-pca-jinja2
cd pcaexample
python setup.py install
initialize_pcaexample_db ./development.ini
pserve ./development.ini

To build the a example of the plugin (pcaplugin) on Linux do:

cd pyramid-pca-jinja2
cd pcaplugin
python setup.py develop
cd ..
cd pcaexample

Edit the configuration of the host application (development.ini) to load the plug-in by uncommenting line 26 to read:

pcaexample.plugins = examplePlugin

Then do:

pserve ./development.ini

Screenshot

Author

Carlos Quiros (cquiros_at_qlands.com / c.f.quiros_at_cgiar.org)