[issue35078] Refactor code in calendar.py module

[Srinivas Reddy Thatiparthy(శ్రీనివాస్ రెడ్డి తాటిపర్తి)]

Change by Srinivas  Reddy Thatiparthy(శ్రీనివాస్ రెడ్డి తాటిపర్తి) <thatiparthysreenivas at gmail.com>:


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title: Allow customization of css class name of a month in  calendar module -> Refactor code in calendar.py module

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35078>
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