There was a talk about using Python with robotics at this years PyConAU called Ah! I see you have the machine that goes ‘BING’! by Dr. Graeme Cross.
The only option he recommended for using Python on a microcontroller board was PyMite which I think also goes by the name of Python-On-A-Chip.
It has been ported to a range of boards – specifically he mentions the Arduino Mega which you said is not an option for you, but it is possible it is supported on other Arduino boards.
However, because it is a “batteries not included” version of Python it is more than likely that you will have a real problem getting numpy/scipy etc up and running.
As other posters have suggested, implementing in C might be the path of least resistence.
Update: again, not specifically for Arduino, but pyMCU looks to provide python on a chip. The author states he may look at developing an Arduino version of pyMCU if there is enough interest.