Started with Let's Encrypt. Running Mac OS X. Failed. Guessed cause has something to do with macports vs homebrew and having the proper Python version active. Disabled macports. Now the app runs.
But I got "Failed to connect to host for DVSNI challenge".
Start googling, reading, messing around with this for a while. No joy.
Bailed on Let's Encrypt, started over with StartSSL, because its the first source of free for not-for-profit certs I found.
Happy to take recommendations for alternatives.