python-gtkclassbuilder is an alternative to Gtk Builder, designed to
ease the making of building blocks within glade.
When it processes a glade file, Gtk Builder gives you back an object --
instances of the widgets described in the file. This makes it
unsuitable for creating generic widgets that you'll use multiple times.
To get another one, you have to process the file all over again.
python-gtkclassbuilder on the other hand, constructs a class, which
like any other widget class, may be instantiated multiple times.
This is still very WIP, but it's possible to do basic things.
examples/ directory for a taste of the api.
LGPL 2.1 or later (The same as Gtk). See