cython/cython

Generalise parallel loops - piter()

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#2,628 opened on Sep 25, 2018

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Cython Language Featurefeaturehelp wanted

Description

Cython currently restricts OpenMP loops to integer iteration using cython.parallel.prange().

A more general cython.parallel.piter() to wrap iterables would allow extending this to C++ iteration, C arrays, bytes/unicode buffers and direct memory view iteration. Except for C++ iteration (which the C++ compiler can handle), all of these cases are mapped to integer iteration internally and would thus be converted to a normal prange() loop by Cython.

Contributor guide

Tech stack
pythonccpp
Domain
performance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Cython internalsOpenMPC/C++ iterationparallel computing concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
The issue proposes adding a `cython.parallel.piter()` function to generalize parallel loops beyond integer iteration. To implement this, first study the existing `prange()` implementation in Cython's source code, likely in the compiler's parallelization module. Then design how `piter()` can map iterables (e.g., C++ containers, C arrays, Python buffers) to integer indices internally, converting them to `prange()` loops. The lack of comments or linked PRs means you would need to open a discussion to clarify the design and ensure it aligns with maintainer expectations.