python에서 Optional(Nullable) type을 다루는 법

https://stackoverflow.com/questions/54612493/whats-the-best-way-to-handle-optional-values-in-python

pep-0505
https://peps.python.org/pep-0505/#the-maybe-dot-and-maybe-subscript-operators

pymaybe
https://github.com/ekampf/pymaybe

other = "some default value" if s is None else s
https://stackoverflow.com/questions/4978738/is-there-a-python-equivalent-of-the-c-sharp-null-coalescing-operator