direnv and mamba for python dev shells

I am a proponent of Nix for stable and reproducible builds of software. Theoretically, it’s all positives: symlink-to-store based environment to allow multiple software (dependency) versions live conflict-free, allow impromptu overrides and custom builds of any package/dependency cool nix-shell (or nix develop) feature for hacking away at your software … and so much more that I don’t care to research and write about.