Running Python on Arduino
To my knowledge, there is not a "python to ATMega architecture" compiler out there. 

However, it's not true that MicroPython only runs on PyBoard. There are versions for installation also on the ESP8266 and ESP32 chips, and so the popular NodeMCU and Wemos D1 development boards, or any of the other similar products with those processors, can easily run Python code. Many of these are available at a very low cost from the usual retailers/sources.

Be aware that MicroPython is somewhat limited compared to the full version due to the limited RAM available on these boards.