Pyhton Script Called by xlwings Addin

[SamT]

VBA doesn't do scripts. VBA does source code. It compiles.
vbs does scripts

As far as your python script, I don't know if anybody here uses Python. Wait and see

However
wb.sheets[0].range('A1').value

Might need to read
wb.sheets[1].range('A1').value

Even better would be to pass the Name of the Worksheet, the numerical index depends on it's tab position.

Also, I am clueless if 'A1' will reach the Excel Workbook as "A1". The lack of capitalization of the Collections will probable by OK.

What is the error in my understanding or my approach?

Hard to say... You haven't given us your entire "approach."