Is that dependency html-1.16 compatible with python 3? It looks like it’s used by that module, either directly or as a transitive dependency, and Pex is failing to get a python 3 compatible build of that version Confirm that version isn’t compatible with python 3. Try going to PyPi and searching for it, looking for version number in the left. Or try

pip3 install html=1.16

Then once you confirm that, you have to find how to get a python 3 version, either by upgrading it or removing it