I have some experience using MicroPython on the PyBoard (not the ESP8266). MicroPython is a very nice implementation of Python 3.X. A few differences because of the need to be extremely parsimonious with RAM usage -- mostly only noticed if trying to inherit from built-in types. Nothing that is onerous to avoid. MicroPython is an outstandingly good project IMHO, with a great community.

Damien George, the creator of MicroPython, is an extraordinarily talented individual. He's also extraordinarily generous having volunteered a substantial block of time and effort to get MicroPython running on the upcoming BBC micro:bit (a million of which will be delivered to the UK's 11 & 12 year olds).