Plugin framework - Overcomplicating things?

André andre.roberge at
Thu Mar 27 12:18:49 CET 2008

On Mar 27, 3:31 am, "Gabriel Genellina" <gagsl-... at>
> En Thu, 27 Mar 2008 01:50:56 -0300, hajdu... at
> <hajdu... at> escribió:
> > All this comes to my question - am I overcomplicating this project? I
> > can understand the use of something like the trac component system if
> > I had multiple components and plugins that handled different areas of
> > my project and different points of interaction, but I don't.  I've got
> > exactly one spot where I want to check all my plugins and hand off the
> > message to which ever ones are looking for that command.
> As you said, it looks like you're really overengineering your design then.
> > So really,
> > should I even bother with trying to setup some framework for this or
> > should I just be doing a simple loop over a directory, importing all
> > the plugins and storing them in a list and then looping over them in
> > the message handler to see which ones were looking for the command and
> > letting them do their thing?

You could set thing up so that there's no need to loop over the
What you can do is register a plugin (as mentioned to you before by
Gabriel - see below) and create an entry in a handler dict so that you
can directly dispatch the message to the appropriate handler without
having to loop over a list of them.  Something like

> That may be an option.
> You may want to setup a simple registry mechanism, so the plugin modules
> look like:
> ### begin ###
> class AVeryNicePlugin(object): #  or perhaps using a suitable base class
>      def handle_message(self, message):
>          ...
>  from plugin import PluginRegistry
> PluginRegistry.register(AVeryNicePlugin)
> ### end ###
> Your application scans a known directory for files ending in ""
> and imports them; the modules register themselves any class (or classes),
> and at appropiate times the application calls some method(s) of the
> registered plugins.

An alternative (which we found simpler with Crunchy) is to not have a
class-based structure, but working with simple modules and functions.
All modules are put in the "plugin" directory which are imported at
the beginning.  Each module contain at least two functions:
1. register() which create the handlers dict entry so that it point
out to the appropriate function.
2. one or more function that is called based on the message received.

Hope it helps,



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