Driving Excel from Python in Windows

We have various spreadsheets that employ deliciously complicated macros and third party extensions to produce complicated models. I’m working on a project that involves slightly tweaking various inputs and seeing the results. Rather than doing this by hand or writing VBA, I’d like to see if I can write a python script to drive this. In other words, the python script will start up, load the excel sheet, and then interact with the sheet by making minor changes in some cells and seeing how they affect other cells.

check if a file is open in Python

In my app, I write to an excel file. After writing, the user is able to view the file by opening it. But if the user forgets to close the file before any further writing, a warning message should appear. So I need a way to check this file is open before the writing process. Could you supply me with some python code to do this task?