You don’t need to write xpcom wrappers to use js objects as xpcom objects unless…the other language needs to createInstance/getService to get the object. If you want to pass a js object from chrome to a pyxpcom instance (in fact any xpcom instance), you only need to be sure your js class implements the functions defined in IDL for the interface you are calling. jsconnect handles the magic for you. We do this all the time in Komodo. Python works similarly, you don’t need to createInstance on a python object to pass it through xpcom, so long as the com_interface is defined in the class. That helps to reduce overhead on the python side.

XPCOM is really not that slow (it’s not blazing fast either) unless you are iterating over something across XPCOM boundaries. We often unwrap the object if it’s a python xpcom object, or rearchitect a bit to avoid those situations. At this point, when we have performance issues, it’s almost never an XPCOM issue.

Using the system python is fine so long as you are not involving binary components or the user builds the components on their system. Mozilla is built with UCS2, linux distros vary between UCS2 and UCS4 for at least the python build. That can cause havoc to say the least. The other issue of course is, the user upgrading some module that then breaks your application.

Small or non-binary based projects may not run into these issues, but they are significant for larger projects that do binary distros. For example, if PyXPCOM were part of Firefox, IMO Firefox would be distributing/embeding python to avoid these issues. Firefox actually has lots of home-grown or embeded code (expat is an example) rather than relying on system provided code to avoid dependencies on external systems.

I chose to package up python with py2exe but take on board your Python as platform thoughts. In my case ease of installation was important and py2exe takes care of all the dependent modules as well plus avoids side-by-sdie python version issues on Windows (only one is the default).

http://www.assembla.com/wiki/show/maavis
http://code.google.com/p/outfox/