Python 3.8 is a recent release, and has performance improvements over previous Python 3.x versions.
Meanwhile PyPy is an alternative Python interpreter built for speed.
Testing with Iron Horse and FIRS:
- Python 3.8 is often 10%-20% faster than Python 3.5
- PyPY is up to 50% faster than Python 3.5 (i.e. it completes an nml run in half the time)
Not everything is faster with PyPy. Compiling docs and generating images are slower for me with PyPy than Python 3.8, but that's my code not nmlc.
For more on PyPy: http://pypy.org/