Gaphas is a Cairo-based canvas API similar to gnome-canvas, ccc, goocanvas and many others. It is written in pure Python, making it a little easier to work with than some of the comparable libraries. It is also written in a very well-laid-out, logical way using high-level Python constructs. It is a modern and extremely extensible piece of code.
The development of Gaphas occurs at http://github.com/amolenaar/gaphas.
The latest release of Gaphas is also usually available using 'easy_install' or via the PyPI site: http://pypi.python.org/pypi/gaphas/.
Gaphas is an integral part of the UML diagramming too, Gaphor.