What is the purpose of PYTHONPATH environment variable?

Answer 1

https://www.tutorialspoint.com/What-is-PYTHONPATH-environment-variable-in-JUMP_LINK__&&__Python__&&__JUMP_LINK
https://docs.python.org/3/using/cmdline.html

Answer 2

PYTHONPATH adds new paths to those that Python uses by default. The common path determines where Python will look for modules when they are imported.