credits: http://www.openbookproject.net/thinkcs/python/english2e/copyright.html

https://krother.gitbooks.io/python-3-basics-tutorial/content/en/data_types/tuples.html

http://www.diveintopython3.net/native-datatypes.html#tuples

http://pymbook.readthedocs.io/en/latest/datastructure.html