anchor.diff:          ${pythonPackages.virtualenv}/bin/virtualenv $VIRTUALENV_ROOT
         fi
         source $VIRTUALENV_ROOT/bin/activate
  -      make requirements${pkgs.stdenv.lib.optionalString forTest "_for_test"}
  +      make requirements${pkgs.stdenv.lib.optionalString forDev "-dev"}
       '';
     }).overrideAttrs (if builtins.pathExists localOverridesPath then (import localOverridesPath args) else (x: x));
   })
  
positive.code:       pkgs.git
        # for `cryptography`
        pkgs.openssl
      ] ++ pkgs.stdenv.lib.optionals forTest ([
          # for lxml
          pkgs.libxml2
          pkgs.libxslt
  
negative.code:   args = rec {
      pkgs = import <nixpkgs> {};
      pythonPackages = pkgs.python36Packages;
      forDev = true;
      localOverridesPath = ./local.nix;
    } // argsOuter;
  in (with args; {
  