Ferret--Mac users,
After that, I installed pyferret on another macOS High Sierra machine of mine, which failed to work. This problem seems to be due to the lack of 100% binary compatibility (perhaps due to dependency on hardware) in some of the pyferret dynamic libraries.
I list the revised steps:
0.1) Install homebrew.
0.2) Install python via homebrew.
1.1) Install miniconda via homebrew: