No module named '_cffi_backend' after compiling Python on a Mac

I'm compiling Pythons using the script here:

https://gist.github.com/13am/a6bb1a1c4803afbf78457a57e0d47dad

This has stopped working in terms of getting a functional OpenSSL, e.g. when compiling Python 3.6.6. I now get the following error when importing from OpenSSL.

from OpenSSL import rand, crypto, SSL

File "/Users/me/lib/python/venv/asunto/lib/python3.6/site-packages/OpenSSL/rand.py", line 12, in from OpenSSL._util import ( File "/Users/me/lib/python/venv/asunto/lib/python3.6/site-packages/OpenSSL/_util.py", line 6, in from cryptography.hazmat.bindings.openssl.binding import Binding File "/Users/me/lib/python/venv/asunto/lib/python3.6/site-packages/cryptography/hazmat/bindings/openssl/binding.py", line 12, in from cryptography.hazmat.bindings._openssl import ffi, lib ModuleNotFoundError: No module named '_cffi_backend'

This may be more related to Homebrew or something else, but compiling like this has been working for a long time and suddenly stopped and I don't know how to fix it. Any ideas?