Help with converting custom container written in python from GTK 2 to 3

[Damien Moore <damienlmoore gmail com>]

Hi,

I've started the long process of converting a large-ish python photo
manager app to GTK3. I've started with one of the more challenging bits of
the program to port, which involves a custom container. Here's a gist of
the non-working version of the GTK3 code, which includes a sample program
to test it:

https://gist.github.com/spillz/20a5e0c789a5238254be

And here's a file which contains the original pygtk2 version (and also
includes a sample test program), which works just fine:

https://github.com/spillz/picty/blob/master/modules/picty/uitools/overlay_widgets.py

The GTK3 code appears to run without error, but I have two problems:
1. The children of the ProportionalLayout don't display on screen. I've
tried adding do_realize and do_draw methods that respectively add a window
and propagate drawing but they don't have any effect.
2. There's an attribute error during the shutdown stage that claims the
ProportionalLayout doesn't have a "children" attribute. (A similar issue
with a custom container has been reported here:
http://stackoverflow.com/questions/21214732/custom-gtk-container-with-pygobject
)

At least for #1, I suspect I am missing something obvious but not sure what
it is.

Any tips would be appreciated.

Thanks!