This was fixed upstream two days ago: https://github.com/fonttools/fonttools/commit/39b02fd2240325af1261d1b57733edbb001d50ea but a new fonttools release has not been made yet.
- Bug#950405: python3-fonttools: warning SyntaxWarning:... Paul Wise
- Bug#950405: python3-fonttools: warning SyntaxWar... James Godfrey-Kittle

