Discourse is written in ruby, so it’s necessary to write a script that interacts with the internals of Discourse. An import is a dev centric proposition.
Every script is full of edges cases. I’ve done over a hundred imports. Every single one has required tweaks for various reasons.
The likelihood that you can write an import script for Discourse in python is very close to zero. If you do, it will likely not work for anyone else. And once you’ve done your migration, you’re not likely to maintain the code for future changes in mybb and discourse.