I pushed a fix for Python 3.9 in commit f08c7cb0c75e7d5305c82d6a4af68ddf74fb08b1. But, we use Python 3.8 for everything, and my patch (attached) fails to apply for some reason. It does work when I apply the new bug fix patch "by hand" onto the Guix source code for our current python-3.8 package.