lxml 4.0 doesn’t build on Mac OS Mojave. But the latest version does. Unfortunately pyinstapaper looks for 4.0 when it builds.

I would have never figured this out but another developer submitted a merge request that noted the lxml issue.

The request hasn’t been accepted yet so if you try to install pyinstapaper using pip it will error out. That said, you can still install pyinstapaper from source (assumes you have jumped through all of the ‘brew install $foo’ requirements stuff) to get python 3.x running on your Mac.

To get pyinstapaper to install:

• Download the the code for this module as a zip file.
• Extract zip.
• Edit the setup.py file and change  the line that reads:
• ‘lxml>=3.4,<=4’, to ‘lxml>=3.4,<=5’,
• save the change and then from within the directory that you downloaded the source run
  ‘python setup.py install’ and you should be good to go.