anchor.diff:    buildInputs = lib.optionals stdenv.isDarwin [ libiconv ];
   
     propagatedBuildInputs = [
  -    hypothesis
       typing-extensions
       typing-inspect
       pyyaml
  -  ] ++ lib.optional (pythonOlder "3.7") [
  -    dataclasses
     ];
   
     checkInputs = [
  +    hypothesis
       pytestCheckHook
     ];
   
  
positive.code: { lib
  , stdenv
  , buildPythonPackage
  , dataclasses
  , fetchFromGitHub
  , hypothesis
  , libiconv
  
negative.code: 
  buildPythonPackage rec {
    pname = "libcst";
    version = "0.4.3";
    format = "pyproject";
  
    disabled = pythonOlder "3.7";
  
    src = fetchFromGitHub {
      owner = "instagram";
      repo = pname;
      rev = "v${version}";
      sha256 = "sha256-Lm62rVL5f+fu4KzOQMroM0Eu27l5v2dkGtRiIVPFNhg=";
    };
  
    cargoDeps = rustPlatform.fetchCargoTarball {
      inherit src;
      sourceRoot = "source/${cargoRoot}";
      name = "${pname}-${version}";
      hash = "sha256-i5BYYiILadKEPIJOaWdG1lZNSHfNQnwmc5j0D1jg/kc=";
    };
  
    cargoRoot = "native";
  