The Python library cgkit already supports Aqsis, Pixie, and 3Delight, by the way. Cycles is also free, open source, and cross-platform, and Cycles seems to be

The Python library cgkit already supports Aqsis, Pixie, and 3Delight, by the way. Cycles is also free, open source, and cross-platform, and Cycles seems to be both further ahead than either Aqsis or Pixie and moving faster. However, it could use someone to make a Python interface for it.