anchor.diff:  { lib
   , buildPythonPackage
   , fetchPypi
  -, isPy27
  +, pythonOlder
   , setuptools-scm
   , pytestCheckHook
   , filelock
  
positive.code:   ];
  
    meta = with lib; {
      description = "py.test xdist plugin for distributed testing and loop-on-failing modes";
      homepage = "https://github.com/pytest-dev/pytest-xdist";
      license = licenses.mit;
      maintainers = with maintainers; [ dotlambda ];
  
negative.code: 
  buildPythonPackage rec {
    pname = "pytest-xdist";
    version = "2.3.0";
    disabled = pythonOlder "3.6";
  
    src = fetchPypi {
      inherit pname version;
      sha256 = "e8ecde2f85d88fbcadb7d28cb33da0fa29bca5cf7d5967fa89fc0e97e5299ea5";
    };
  
    nativeBuildInputs = [ setuptools-scm ];
  