Drawing vector diagrams with Python

What's the easiest way to draw nice vector diagrams with Python? I was asked this question some time ago by a bioinformatician who was moving from Perl to Python, and previously used the gd library. gd was widely used back in the day, but looks a bit clunky now.

Here's the solution I came up with, to use SVG through PySVG. It's pure-Python and so doesn't require any extra libraries, which is always a pain when dealing with graphics.

I used the code below to generate an SVG file, which was converted to the above PNG with Inkscape:
Anyone else got any suggestions?