> It is definitely possible with Nix to use the precise versions of what's in your requirements.txt, but I'm not sure if the Nixpkgs maintainers would allow all that extra duplication upstream.
They do for end user applications, but not for Python libraries. The libraries in Nixpkgs are expected to be interoperable, which requires converging certain versions because otherwise transitive dependencies on varying library versions mean that libraries used together are subject to serious, mysterious bugs. But applications packaged in Nixpkgs can pull in an exact set of libraries of their own if that's what it takes for them to run reliably.
They do for end user applications, but not for Python libraries. The libraries in Nixpkgs are expected to be interoperable, which requires converging certain versions because otherwise transitive dependencies on varying library versions mean that libraries used together are subject to serious, mysterious bugs. But applications packaged in Nixpkgs can pull in an exact set of libraries of their own if that's what it takes for them to run reliably.