Or, if you have some "launch" app, like for instance launcher, you can launch Pythonista from the today/notifications center (where launcher is a widget), asking Pythonista to directly run a particular script.

I define all my scripts in this way, so, they have their own icon and they all do this:

launch Pythonista create an empty panel as background to hide the Pythonista script process terminate by "crashing" to go back to the home screen

If they run in the share sheet, they don't end by crash but by closing the appex mode.