This is a bit of a hack, but it works for people who want to use MacOS and Python 3 for the project.
I think in the future this solution could be changed by writing a script that automatically finds python and boost locations and edits the RenderMan.jucer XML file.
Use RenderMan-py36.jucer to build and follow instructions outlined at https://github.com/fedden/RenderMan/issues/7\#issuecomment-375697319.
This is a bit of a hack, but it works for people who want to use MacOS and Python 3 for the project.
I think in the future this solution could be changed by writing a script that automatically finds python and boost locations and edits the RenderMan.jucer XML file.