I ran into a crash on lxml 4.3.1 (released not too long ago it seems), pulled in via pip, on travis. We had not pinned my dependency version, so we went from 4.3.0 to 4.3.1, and all our builds started failing.

This can be reproduced deterministically (on travis and also on my local linux machine), by doing:

git clone git@github.com:WebAudio/web-audio-api.git

git clone https://github.com/tabatkins/bikeshed.git
pip install --editable $PWD/bikeshed
bikeshed update

cd web-audio-api

bikeshed --print=plain -f spec

Let me know if I can help debugging this, I've posted some background info on https://github.com/WebAudio/web-audio-api/pull/1830#issuecomment-465229675

Thanks,

Paul.