pep cleanup for the file weyl_group.py

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Component: **combinatorics**

Author: **Frédéric Chapoton**

Branch/Commit: **[`f83a25d`](https://github.com/sagemath/sagetrac-mirror/commit/f83a25d0400626a5561c76ec837e58abc8ac5262)**

Reviewer: **David Coudert**

_Issue created by migration from https://trac.sagemath.org/ticket/34620_

