Quickly reload nix expression in nix-shell? When I run nix-shell ` nix-shell ~/dev/nixpkgs -A pythonPackages.some-package ` and then edit phases of `pythonPackages.some-package`, how to reload `nix-shell` environment with new changes? Quit `nix-shell` and rerun is one option, but are there alternatives?

No other simple options, sorry. I can only think of rewriting nix-shell to accomplish what you want. Probably it's not even that hard. Reparse the expression, cleanup the env and refill the env.