A former boss of mine had a sign on the wall in his office that said, “Out there, right now, someone is writing a queue and getting it wrong.”  What he meant was that if you’re using a mature language like Java or Python, you should never have to deal with textbook data structures, dates and times, currencies, and other things directly: someone else will always have been there first.  So, if you find yourself wrestling with timezones or passwords, fire up your favorite search engine and see what it turns up.