[pygtk] Cannot subclass gtk.Widget

[Jeffrey Barish]

I am trying to create a custom widget.  Following examples I found from a
Google search, I am trying to subclass gtk.Widget.  I get the error
message:

TypeError: cannot create instance of abstract (non-instantiable) type
`GtkWidget'

A further search suggests that I might have a version problem, but I am
running 2.10.3 of PyGTK and 2.10.6 of libgtk, which would seem to be plenty
new enough.

I also cannot subclass Container or Box, but HBox works.
-- 
Jeffrey Barish