The Python interpreter is software that compiles and runs applications that developers create. It also handles importing additional libraries and all syntax for the language itself.
SR OS provides the MicroPython interpreter on the SR OS node. This interpreter implements Python 3.4 and is designed to operate using a small memory footprint, which allows SR OS to launch multiple interpreters in parallel.
The Python 3 interpreter is called by the SR OS function that requires it; for example, the MD-CLI. The interpreter is not called directly by the operator.