It’s a Pluggable World

One of the new additions in TG2.1.4 has been the support for the so called pluggable applications, this is a really powerful and convenient feature that probably not enough TurboGears users started embracing.

For people that never used them, pluggable applications provide a python package that can be installed and “plugged” inside any existing TurboGears application to add new features. Django has been probably the first framework to bring this feature to Python world and TurboGears implementation tries to be as convenient by making pluggable applications identical to plain TurboGears applications and providing a “quickstart-pluggable” command that creates the application skeleton for you. Pluggable applications can be installed using easy_install or pip and they can off course depend on any other pluggable application they need.

This year, at EuroPython 2012, I have been pleased to present a talk about using TurboGears for rapid prototyping (both in Italian and English, you should be able to find the videos on EuroPython youtube channel), so I decided to dedicate a part of it to pluggable applications as they are actually the fastest way to rapidly prototype a project. With my surprise most the questions I received were about the EasyCrudRestController and not about pluggable applications.

While the EasyCrudRestController is definitively a powerful tool, it’s far from being the answer to all the web developments needs. In most of the applications you are going to develop, users will probably prefer consulting content from something more engaging than an administration table of database entries.

This month, to create a set of utilities that can help people with their everyday needs, I decided to ask guys that work with me to make every part of the web sites that they were writing as pluggable applications. The result of this experiment has been that most of the pluggable apps that I did in my spare time (tgapp-smallpress, tgapp-photos, tgapp-tgcomments, tgext.tagging and so on) ended being used in real world projects and started to improve exposing hooks and ways to customize their behavior for the project they were going to be used.

After a few weeks, new pluggables like tgapp-fbauth, tgapp-userprofile, tgapp-calendarevents, tgapp-fbcontest, tgapp-youtubevideo has seen light and developing the target application started becoming blazing fast: Just plug what you need and customize it.

Embracing this philosophy the last project I’m working on has an app_cfg.py file that looks like:

plug(base_config, 'tgext.debugbar', inventing=True)
plug(base_config, 'tgext.scss')
plug(base_config, 'tgext.browserlimit')
plug(base_config, 'registration')
plug(base_config, 'photos')
plug(base_config, 'smallpress', 'press', form='XXX.lib.forms.ArticleForm')
plug(base_config, 'tgcomments', allow_anonymous=False)
from XXX.lib.matches import MyKindOfEvent
plug(base_config, 'calendarevents', 'eventi', event_types=[MyKindOfEvent()])
replace_template(base_config, 'smallpress.templates.article', 
                              'XXX.templates.press.article')
replace_template(base_config, 'smallpress.templates.excerpt', 
                              'XXX.templates.press.excerpt')

Thanks to this our development process has really improved: whenever a developer finds a bug he just has to propose a patch for the target pluggable, whenever someone notices a missing index on a query he has just to add it to the given pluggable. All the websites under development improved like people were working on the same project.

While existing pluggables might be limited, buggy or slow I’m getting confident that they will continue to improve, and some day they will surpass whatever custom implementation I can think of. I think I’m going to heavily rely on pluggable applications for any future project sticking to only one rule: “make it opensource”. This way, apart from probably helping other people, I’m also improving my own projects through other people feedbacks, bug reports and patches to the pluggables I used.

So, next time you have to start a new project give a look at the TurboGears CogBin and check if there is a pluggable application that looks like what you need. If you find any issue or find space for improvements just fork it and send a pull request, or send an email on the TurboGears Mailing List I’ll do my best to address any reported issue thanking you for your feedbacks as I’m aware that you are actually improving any past and future project that relies on that pluggable.

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