anchor.diff: -{ lib
  +{ async_generator
   , buildPythonPackage
  -, fetchPypi
  -, pythonOlder
  -, async_generator
  -, traitlets
  +, fetchFromGitHub
  +, ipykernel
  +, ipywidgets
  +, jupyter-client
  +, lib
  +, nbconvert
   , nbformat
   , nest-asyncio
  -, jupyter-client
  +, pytest-asyncio
   , pytestCheckHook
  +, pythonOlder
  +, traitlets
   , xmltodict
  -, nbconvert
  -, ipywidgets
   }:
   
   let nbclient = buildPythonPackage rec {
  
positive.code:   # circular dependencies if enabled by default
    doCheck = false;
  
    checkInputs = [ pytestCheckHook xmltodict nbconvert ipywidgets ];
  
    preCheck = ''
      export HOME=$(mktemp -d)
  
negative.code: 
    disabled = pythonOlder "3.7";
  
    src = fetchFromGitHub {
      owner = "jupyter";
      repo = pname;
      rev = "refs/tags/v${version}";
      hash = "sha256-ofyJNJeNkXbZ9qHLTuzJ13PgEXU9lDQ9NkT4nG/R8Ic=";
    };
  
    propagatedBuildInputs = [ async_generator traitlets nbformat nest-asyncio jupyter-client ];
  