[Python-ideas] More general "for" loop handling

[Joseph Martinot-Lagarde]

Le 03/05/2015 23:52, Joseph Martinot-Lagarde a écrit :
> Le 02/05/2015 18:16, Andrew Barnert via Python-ideas a écrit :
>> On May 1, 2015, at 08:52, Joseph Martinot-Lagarde
>> <joseph.martinot-lagarde at 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:
>>
>> I think that's pretty good evidence that this proposal (I meant the
>> syntax for loop modifiers, not "some way to do loops in parallel would
>> be nice") isn't needed. What OpenMP has to do with loop modifier
>> syntax, Cython can do with just a special iterator in normal Python
>> syntax.
>
> Cython uses python syntax but the behavior is different. This is
> especially obvious seeing how break and return are managed, where the
> difference in not only in the iterator.
>
Sorry, ignore my last email. I agree that no new *syntax* is needed.
>>
>> Of course that doesn't guarantee that something similar to prange
>> could be built for Python 3.5's Pool, Executor, etc. types without
>> changes, but if even if it can't, a change to the iterator protocol to
>> make prange bulldable doesn't seem as disruptive as a change to the
>> basic syntax of the for loop. (Unless there just is no reasonable
>> change to the protocol that could work.)
>>
>>> 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
>>>
>>> Joseph
>>>
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>
>
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