Writing a Caja-Python extension is a fairly straight-forward process. One simply imports the Caja module from the gobject introspection repository and creates a class which is derived from a gobject.GObject and one of the Caja module's classes. When an extension derives a class, it becomes a "provider", telling Caja to ask it for information. There are several types of providers available for extensions to use: there is MenuProvider, LocationWidgetProvider, ColumnProvider, PropertyPageProvider, and InfoProvider, all of which will be explained in more detail below. Your class can be derived from multiple providers.
Here are the basic steps:
1. A script is written and installed to the standard caja-python extension install path
2. Caja is (re)started and loads the caja-python C extension, which in turn loads all python extensions it can find
3. Any python script in the standard caja-python extension install path that imports the Caja module from the gobject introspection repository and derives the main class from a Caja module class will be loaded
As of caja-python 0.7.0 (and continued in 1.0+), caja-python looks in ~/.local/share/caja-python/extensions for local extensions and $PREFIX/share/caja-python/extensions for global extensions.
1. We no longer support the "import caja" command that previous versions used. This is because caja-python now directly uses Caja's annotations, which must be imported by the "from gi.repository import Caja" command.
2. The extension class must now derive itself from a gobject.GObject in addition to the standard Caja classes.
3. For now, some Caja class constructors require passing named arguments instead of a standard argument list. This requirement may go away at some point.