Subclassing by monkey-patching

[Jason]

I'm attempting to implement a recursive directory monitor based on the
GIO file monitor in PyGTK. My approach is basically to take the
gio.FileMonitor returned by the method gio.File.monitor_directory(),
connect to the "changed" signal, and add or remove monitors on create/
delete events for subdirectories.

I'd really like to do this by subclassing gio.FileMonitor. But the
problem I'm having is that it's never explicitly initialised in user
code (but somewhere in gio.File.monitor_directory() ). So there's no
point in just declaring a subclass — where would I actually create an
instance?

Is there a way I can write the subclass but then somehow... extend an
existing instance all at once rather than monkeypatch methods on one
by one? So I could take an existing instance of a FileMonitor and make
it an instance of my subclass? This would even allow me to override
the gio.File.monitor_directory() method to take the monitor returned
by the original method and decide whether to make it recursive based
on a parameter passed to monitor_directory().

Cheers,
Jason

PS. Asked a similar question on the pygtk list a few days ago:
http://www.daa.com.au/pipermail/pygtk/2010-September/018965.html