On Fri, May 1, 2015 at 8:52 AM, Joseph Martinot-Lagarde <joseph.martinot-lagarde@m4x.org> wrote:

Le 01/05/2015 02:35, Steven D'Aprano a écrit :

If you still wish to argue for this, one thing which may help your case
is if you can identify other programming languages that have already
done something similar.

Cython has prange. It replaces range() in the for loop but runs the loop body in parallel using openmp:

from cython.parallel import prange

cdef int func(Py_ssize_t n):
cdef Py_ssize_t i

for i in prange(n, nogil=True):
if i == 8:
with gil:
raise Exception()
elif i == 4:
break
elif i == 2:
return i

This is an example from the cython documentation: http://docs.cython.org/src/userguide/parallelism.html

Interesting. I'm trying to imagine how this could be implemented in CPython by turning the for-loop body into a coroutine. It would be a complicated transformation because of the interaction with local variables in the code surrounding the for-loop. Perhaps the compiler could mark all such variables as implicitly nonlocal. The Cython example also shows other interesting issues -- what should return or break do?

In any case, I don't want this idea to distract the PEP 492 discussion -- it's a much thornier problem, and maybe coroutine concurrency isn't what we should be after here -- the use cases here seem to be true (GIL-free) parallelism. I'm imagining that pyparallel has already solved this (if it has solved anything :-).

--Guido van Rossum (python.org/~guido)