DiaCanvas2 has a Python wrapper. The Python layer is based on the PyGTK and Gnome-Python libraries written by James Henstridge.
When you use Python you no longer need to care about references and stuff, so you can focus on making pretty programs instead.
#!/usr/bin/env python
import pygtk
pygtk.require('2.0')
import gtk
import diacanvas
canvas = diacanvas.Canvas()
box = diacanvas.CanvasBox()
box.set(border_width=0.3, color=diacanvas.color(200, 100, 100, 128))
canvas.root.add(box)
box.move(20, 20)
window = gtk.Window()
view = diacanvas.CanvasView(canvas=canvas)
view.show()
window.add(view)
window.connect("destroy", gtk.mainquit)
window.show()
gtk.main()
