anchor.diff:  { lib, buildPythonPackage, pythonOlder, fetchPypi, isPy3k, isPyPy
  -, pythonAtLeast, fetchpatch
   , atomicwrites
   , attrs
   , hypothesis
  
positive.code:     py
      setuptools
      six
      toml
      wcwidth
    ] ++ lib.optionals (pythonOlder "3.6") [ pathlib2 ];
  
  
negative.code: , setuptools
  , setuptools-scm
  , six
  , tomli
  , wcwidth
  , writeText
  }:
  
  buildPythonPackage rec {
    pname = "pytest";
    version = "7.0.1";
    disabled = !isPy3k;
  
    src = fetchPypi {
      inherit pname version;
      sha256 = "sha256-4wkFoMEx09lLiWJKHMWv7D4LovvbFRhn2ODr1JhQ8XE=";
    };
  
    nativeBuildInputs = [ setuptools-scm ];
  
  