Question on calendar derivation logic in the Python module https://pypi.org/project/pandas-market-calendars/. Does this module depend on any third party API's to get the calendars or the calendars are derived based on rules within the code?
There is no communication with a third party API, everything is hardcoded.
You can easily see this in the source code.
There is a calendars folder with definitions of each calendar (see for example the file for ASX).
The project's documentation also mentions that:
As of v2.0 this package provides a mirror of all the calendars from the exchange_calendars package, which itself is the now maintained fork of the original trading_calendars package. This adds over 50 calendars.
There is a list of available calendars here