core/pkgs/build-support/fetchpypilegacy/default.nix

# Fetch from PyPi legacy API as documented in https://warehouse.pypa.io/api-reference/legacy.html
{
  runCommand,
  lib,
  python3,
}:
{
  # package name
  pname,
  # Package index
  url ? null,
  # Multiple package indices to consider
  urls ? [ ],
  # filename including extension
  file,
  # SRI hash
  hash,
  # allow overriding the derivation name
  name ? null,
}:
let
  urls' = urls ++ lib.optional (url != null) url;

  pathParts = lib.filter ({ prefix, path }: "NETRC" == prefix) builtins.nixPath;
  netrc_file = if (pathParts != [ ]) then (lib.head pathParts).path else "";

in
# Assert that we have at least one URL
assert urls' != [ ];
runCommand file
  (
    {
      nativeBuildInputs = [ python3 ];
      impureEnvVars = lib.fetchers.proxyImpureEnvVars;
      outputHashMode = "flat";
      # if hash is empty select a default algo to let nix propose the actual hash.
      outputHashAlgo = if hash == "" then "sha256" else null;
      outputHash = hash;
      NETRC = netrc_file;
    }
    // (lib.optionalAttrs (name != null) { inherit name; })
  )
  ''
    python ${./fetch-legacy.py} ${
      lib.concatStringsSep " " (map (url: "--url ${lib.escapeShellArg url}") urls')
    } --pname ${pname} --filename ${file}
    mv ${file} $out
  ''