sources used for PyBank: https://stackoverflow.com/questions/2400840/python-finding-differences-between-elements-of-a-list https://stackoverflow.com/questions/2612802/how-do-i-clone-a-list-so-that-it-doesnt-change-unexpectedly-after-assignment, https://www.w3schools.com/python/ref_file_write.asp
sources used for PyPoll: sources:https://datagy.io/python-count-unique-values-list/