python3Packages.mkPythonMetaPackage: init

Do pay attention to passing in the right Python version!

#### `mkPythonMetaPackage` function {#mkpythonmetapackage-function}

This will create a meta package containing [metadata files](https://packaging.python.org/en/latest/specifications/recording-installed-packages/) to satisfy a dependency on a package, without it actually having been installed into the environment.

In nixpkgs this is used to package Python packages with split binary/source distributions such as [psycopg2](https://pypi.org/project/psycopg2/)/[psycopg2-binary](https://pypi.org/project/psycopg2-binary/).

```nix

mkPythonMetaPackage {

  pname = "pscycopg2-binary";

  inherit (psycopg2) optional-dependencies version meta;

  dependencies = [ psycopg2 ];

}

```

#### `python.buildEnv` function {#python.buildenv-function}

Python environments can be created using the low-level `pkgs.buildEnv` function.

{

  buildPythonPackage,

  lib,

  hatchling,

}:

{

  pname,

  version,

  dependencies ? [ ],

  optional-dependencies ? { },

  passthru ? { },

  meta ? { },

}:

# Create a "fake" meta package to satisfy a dependency on a package, but don't actually build it.

# This is useful for packages that have a split binary/source dichotomy like psycopg2/psycopg2-binary,

# where we want to use the former, but some projects declare a dependency on the latter.

buildPythonPackage {

  inherit

    pname

    version

    dependencies

    optional-dependencies

    meta

    passthru

    ;

  pyproject = true;

  # Make a minimal pyproject.toml that can be built

  unpackPhase = ''

    cat > pyproject.toml << EOF

    [project]

    name = "${pname}"

    version = "${version}"

    dependencies = ${builtins.toJSON (map lib.getName dependencies)}

    [project.optional-dependencies]

    ${lib.optionalString (optional-dependencies != { }) (

      (lib.concatStringsSep "\n" (

        lib.mapAttrsToList (

          group: deps: group + " = " + builtins.toJSON (map lib.getName deps)

        ) optional-dependencies

      ))

    )}

    [tool.hatch.build.targets.wheel]

    bypass-selection = true

    [build-system]

    requires = ["hatchling"]

    build-backend = "hatchling.build"

    EOF

  '';

  build-system = [ hatchling ];

}

  removePythonPrefix = lib.removePrefix namePrefix;

  mkPythonMetaPackage = callPackage ./meta-package.nix { };

  # Convert derivation to a Python module.

  toPythonModule = drv:

    drv.overrideAttrs( oldAttrs: {

  inherit buildPythonPackage buildPythonApplication;

  inherit hasPythonModule requiredPythonModules makePythonPath disabled disabledIf;

  inherit toPythonModule toPythonApplication;

  inherit mkPythonMetaPackage;

  python = toPythonModule python;