I ran Larry Hastings' Gilectomy testprogram x.py: fib(40) on 8 threads HW: MacBook Pro, 2015, 8 (4+4) cores, 1Gb RAM
Jython ran the program 8 times faster, utilising all 8 cores >95%. Python ran on 1-2 cores less than 60% utilisation. (Pretty sure Jython will run 16 times faster on 16 cores)
It's 2017, why this is acceptable to GvR and the Python community is beyond me.
Jython: real 1m4.959s user 7m38.521s sys 0m2.396s
Python: real 8m19.035s user 8m16.508s sys 0m11.424s