Python: module for plotting Gantt charts

You should also check faces, it's a powerful and free project management tool that you program with python. It's also built in python. It can output many different charts, including gantt chart.

ChartDirector is pretty good at generating advanced charts of all kinds. It has decent python bindings, but it's, unfortunately, not native python or open source in general.

There are actually some Gantt chart examples/screenshots. The code also includes python demo's for building gantt charts.

If you're working on a web application, you can also consider Google Chart. It appears to be flexible/advanced enough for simple, Gantt-like charts. You can read more on this here, for example. Or just google for "google chart gantt"