anchor.diff: -{ buildPythonPackage
  +{ lib
  +, buildPythonPackage
   , fetchFromGitHub
  -, fetchPypi
   , git
  -, isPy27
  -, lib
  +, pythonOlder
   , pytestCheckHook
   , ruamel_yaml
   , toml
  
positive.code: 
  buildPythonPackage rec {
    pname = "pre-commit-hooks";
    version = "3.4.0";
    disabled = isPy27;
  
    # fetchPypi does not provide tests
    src = fetchFromGitHub {
      owner = "pre-commit";
      repo = pname;
      rev = "v${version}";
      sha256 = "1aqkmprdc2lhds9c59pkkf2js65j63197flanaggk7cm8k0kz7zs";
    };
  
    propagatedBuildInputs = [ toml ruamel_yaml ];
    checkInputs = [ git pytestCheckHook ];
  
    # the tests require a functional git installation which requires a valid HOME
    # directory.
  
negative.code:     git config --global user.email "nix-builder@nixos.org"
    '';
  
    pythonImportsCheck = [ "pre_commit_hooks" ];
  
    meta = with lib; {
      description = "Some out-of-the-box hooks for pre-commit";
      homepage = "https://github.com/pre-commit/pre-commit-hooks";
  