Python 3.5 added the infix matrix multiplication operator PEP 465.

This ticket adds support for it in the coercion model.

The infix matrix multiplication operator (@) could be used for matrix and tensor multiplication.

Follow-up: #30244

CC: @jpflori @embray @tscrim @egourgoulhon @mjungmath

Component: python3

Author: Jeroen Demeyer, Matthias Koeppe

Branch/Commit: d939b2c

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/22760