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 <i>extremely</i> 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.