anchor.diff:      sha256 = "8864c29aa344f7ac26eeb94788798f2d0cc791dcf95c632da8d79ebc580e114c";
     };
   
  +  # for the optional dependency ipykernel, only versions < 6 are
  +  # supported, so it's not included in the tests, and not propagated
     propagatedBuildInputs = [ traits apptools setuptools ];
   
     preCheck = ''
  
positive.code:   '';
  
    checkInputs = [
      ipykernel ipython pytestCheckHook
    ];
  
    meta = with lib; {
  
negative.code: { lib, fetchPypi, isPy27
  , buildPythonPackage
  , traits, apptools, pytestCheckHook
  , ipython, setuptools
  }:
  
  buildPythonPackage rec {
  