Python to excel, openpyxl and file format not valid

From here: https://openpyxl.readthedocs.io/en/default/tutorial.html#saving-to-a-file

Note

The following will fail:

>>> wb = load_workbook('document.xlsx')
>>> # Need to save with the extension *.xlsx
>>> wb.save('new_document.xlsm')
>>> # MS Excel can't open the document
>>>
>>> # or
>>>
>>> # Need specify attribute keep_vba=True
>>> wb = load_workbook('document.xlsm')
>>> wb.save('new_document.xlsm')
>>> # MS Excel can't open the document
>>>
>>> # or
>>>
>>> wb = load_workbook('document.xltm', keep_vba=True)
>>> # If us need template document, then we need specify extension as *.xltm.
>>> # If us need document, then we need specify attribute as_template=False.
>>> wb.save('new_document.xlsm', as_template=True)
>>> # MS Excel can't open the document