> How do transitive dependencies in the Python ecosystem work, then?

Not very well.

> how do you prevent everything from grinding to a halt?

I don't have a good answer for you.

> Is there no semantic versioning?

You can read django release process here [1], not sure how it's relevant. I'm not the maintainer of django, but of a project using django. Would it be better if all software was perfect, had no bugs and used perfect semantic versioning? Yes, I would say so. Is that a requirement for using nixpkgs?

> Nixpkgs has its reasons for minimizing redundant packages, however it is certainly possible to package your app with Nix and use the exact specified dependencies.

I'm not packaging it, someone else is, it breaks and they come to the project to raise invalid bug reports.

[1] https://docs.djangoproject.com/en/dev/internals/release-proc...