sage

b1ba78af - gh-36140: python-style loops in `partn_ref.data_structures` (partial) + some pep8

gh-36140: python-style loops in `partn_ref.data_structures` (partial) + some pep8 This converts some loops to the python style. Plus a few pep8 details fixed ### :memo: Checklist - [x] The title is concise, informative, and self-explanatory. - [x] The description explains in detail what this PR is about. URL: https://github.com/sagemath/sage/pull/36140 Reported by: Frédéric Chapoton Reviewer(s):