It doesn't make much sense to run a script/file in an interactive interpreter. If you just want to send text to the Python REPL, then start the repl by running `python` in the builtin terminal and then use the `Send selection to Terminal` menu item/keybinding. If you just want to execute your script, just set the option to run command in VTE and it will just run your script when you execute it.
Maybe if you could explain exactly step by step in detail what you want to be able to do, and what the result should be, it would help clarify.