anchor.diff:  
     # propagate python/setuptools to active setup-hook in nix-shell
     propagatedBuildInputs = propagatedBuildInputs ++ [ python setuptools ];
  -
  -  pythonPath = pythonPath;
   
     configurePhase = attrs.configurePhase or ''
       runHook preConfigure
  
positive.code: , buildInputs ? []
  
  # propagate build dependencies so in case we have A -> B -> C,
  # C can import propagated packages by A
  , propagatedBuildInputs ? []
  
  # passed to "python setup.py build"
  # https://github.com/pypa/pip/issues/881
  , setupPyBuildFlags ? []
  
  
negative.code:     runHook postConfigure
    '';
  
    # we copy nix_run_setup.py over so it's executed relative to the root of the source
    # many project make that assumption
    buildPhase = attrs.buildPhase or ''
      runHook preBuild
      cp ${setuppy} nix_run_setup.py
  