The vast majority of people who write Python code and use Arduino do it the easy way: they run Python on a laptop or some other "big" computer. Their python program communicates over the serial port to an Arduino; the Arduino runs a sketch such as 2B or Firmata. See interfacing.python, SymbianS60Python, etc.
On this page we discuss an alternative:
A few people are experimenting with running Python code directly on the Arduino, so it runs even when the Arduino is "stand-alone", not connected to any other computer. (Python runs as an Interpreted Languages).
The python-on-a-chip interpreter, code name Pymite, runs on the Arduino Mega.
FIXME: put a step-by-step tutorial on this page, not just a link to one.