What is the easiest way to run a python script from google sheets, or alternatively execute the python script when the google sheets opens?
I'm assuming you have some python asset that you would like to use to modify data on Google Sheets. If that's the case, then I think your best option is to use Google APIs to access Google Sheets from python. You can use any of the following two tutorials by Twilio to achieve that. 
If you want to add the python asset into Google sheets (Ex. as a custom function), then it will be much easier to rewrite it in JS.
Execute python script from within google sheets