[issue38539] Update demo files

[Julin]

Julin <julinshaji02 at gmail.com> added the comment:

Okay. While I'm at it, can I make a few minor change as well? Like

 - Use fstrings
 - change range(0, val) to range(val) as range()'s first argument has default value 0.
 - Change `for i in range(len(groups)):` to enumerated (redemo.py)
 - rename ss1.py to spreadsheet.py (to make its purpose clearer)

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<https://bugs.python.org/issue38539>
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