A simple plugin system for Python applications
Quick links:
.. toctree:: :maxdepth: 1 IPlugin PluginManager PluginInfo Extensions Advices
On this page
.. automodule:: yapsy :members: :undoc-members:
For applications that require the plugins and their managers to be more sophisticated, several techniques make such enhancement easy. The following sections detail the most frequent needs for extensions and what you can do about it.
You can define a plugin class with a richer interface than
IPlugin, so long as it inherits from IPlugin, it should work the
same. The only thing you need to know is that the plugin instance is
accessible via the PluginInfo instance from its
PluginInfo.plugin_object.
It is also possible to define a wider variety of plugins, by defining as much subclasses of IPlugin. But in such a case you have to inform the manager about that before collecting plugins:
# Build the manager
simplePluginManager = PluginManager()
# Tell it the default place(s) where to find plugins
simplePluginManager.setPluginPlaces(["path/to/myplugins"])
# Define the various categories corresponding to the different
# kinds of plugins you have defined
simplePluginManager.setCategoriesFilter({
"Playback" : IPlaybackPlugin,
"SongInfo" : ISongInfoPlugin,
"Visualization" : IVisualisation,
})
Note
Communicating with the plugins belonging to a given category might then be achieved with some code looking like the following:
# Trigger 'some action' from the "Visualization" plugins
for pluginInfo in simplePluginManager.getPluginsOfCategory("Visualization"):
pluginInfo.plugin_object.doSomething(...)
To make the plugin manager more helpful to the other components of an application, you should consider decorating it.
Actually a "template" for such decoration is provided as :doc:`PluginManagerDecorator`, which must be inherited in order to implement the right decorator for your application.
Such decorators can be chained, so that you can take advantage of the ready-made decorators such as:
:doc:`ConfigurablePluginManager`
Implements a PluginManager that uses a configuration file to
save the plugins to be activated by default and also grants access
to this file to the plugins.
:doc:`AutoInstallPluginManager`
Automatically copy the plugin files to the right plugin directory.
A full list of pre-implemented decorators is available at :doc:`Extensions`.
By default, plugins are described by a text file called the plugin "info file" expected to have a ".yapsy-plugin" extension.
You may want to use another way to describe and detect your
application's plugin and happily yapsy (since version 1.10) makes it
possible to provide the PluginManager with a custom strategy for
plugin detection.
See :doc:`IPluginLocator` for the required interface of such strategies and :doc:`PluginFileLocator` for a working example of such a detection strategy.
To tweak the plugin loading phase it is highly advised to re-implement your own manager class.
The nice thing is, if your new manager inherits PluginManager, then it will naturally fit as the start point of any decoration chain. You just have to provide an instance of this new manager to the first decorators, like in the following:
# build and configure a specific manager baseManager = MyNewManager() # start decorating this manager to add some more responsibilities myFirstDecorator = AFirstPluginManagerDecorator(baseManager) # add even more stuff mySecondDecorator = ASecondPluginManagerDecorator(myFirstDecorator)
Note
Some decorators have been implemented that modify the way plugins are loaded, this is however not the easiest way to do it and it makes it harder to build a chain of decoration that would include these decorators. Among those are :doc:`VersionedPluginManager` and :doc:`FilteredPluginManager`
Yapsy 's development has been originally motivated by the MathBench project but it is now used in other (more advanced) projects like:
- peppy : "an XEmacs-like editor in Python. Eventually. "
- MysteryMachine : "an application for writing freeform games."
- Aranduka : "A simple e-book manager and reader"
- err : "a plugin based chatbot"
- nikola : "a Static Site and Blog Generator"
Nowadays, the development is clearly motivated by such external projects and the enthusiast developpers who use the library.
If you're interested in using yapsy, feel free to look into the following links:
- :doc:`Advices`
- A minimal example on stackoverflow
- Making your app modular: Yapsy (applied to Qt apps)
- Python plugins with yapsy (applied to GTK apps)
You're always welcome if you suggest any kind of enhancements, any new decorators or any new pluginmanager. Even more if there is some code coming with it though this is absolutely not compulsory.
It is also really fine to fork the code ! In the past, some people found Yapsy just good enough to be used as a "code base" for their own plugin system, which they evolved in a more or less incompatible way with the "original" Yapsy, if you think about it, with such a small library this is actually a clever thing to do.
In any case, please remember that just providing some feedback on where you're using Yapsy (original or forked) and how it is useful to you, is in itself a appreciable contribution :)
The work is placed under the simplified BSD license in order to make it as easy as possible to be reused in other projects.
Please note that the icon is not under the same license but under the Creative Common Attribution-ShareAlike license.
The project is hosted on GitHub.
To use pip for a development install you can do something like:
pip install -e "git+https://github.com/tibonihoo/yapsy.git#egg=yapsy&subdirectory=package"A development version of the documentation is available on ReadTheDoc.
Other Python plugin systems already existed before Yapsy and some have appeared after that. Yapsy's creation is by no mean a sign that these others plugin systems sucks :) It is just the results of me being slighlty lazy and as I had already a good idea of how a simple plugin system should look like, I wanted to implement my own [1].
- setuptools seems to be designed to allow applications to have a plugin system.
- Sprinkles seems to be also quite lightweight and simple but just maybe too far away from the design I had in mind.
- PlugBoard is certainly quite good also but too complex for me. It also depends on zope which considered what I want to do here is way too much.
- Marty Alchin's simple plugin framework is a quite interesting description of a plugin architecture with code snippets as illustrations.
- stevedor looks quite promising and actually seems to make setuptools relevant to build plugin systems.
- You can look up more example on a stackoverflow's discution about minimal plugin systems in Python
| [1] | All the more because it seems that my modest design ideas slightly differ from what has been done in other libraries. |