Added a shell.nix file to project directory. Run

nix-shell and this will create the necessary Python
3.12 environment needed to run the python script on
a NixOS (25.11) system.

shell.nix

@@ -7,6 +7,7 @@ pkgs.mkShell {
         numpy
         openpyxl
         pandas
+        python-dateutil
     ]))
   ];
 }