packages
pyproject.nix
's package set is much smaller and more narrow in scope than nixpkgs.
It's purpose is only to package build-system dependencies, which are missing from Python package manager lock files, so needs to be supplemented from elsewhere.
It is not meant to be a general purpose Python set, only something for lock file consumers to build on top of.
Creating a base package set
# Returns a scope with base packages.
pkgs.callPackage pyproject-nix.build.packages {
python = interpreter;
}
Overriding scope
See the nixpkgs documentation.