Iterables and Iterators

http://treyhunner.com/2018/02/python-range-is-not-an-iterator/

http://treyhunner.com/2016/12/python-iterator-protocol-how-for-loops-work/?__s=qspqufpbr6tqtqyvqmba

Loop better: A deeper look at iteration in Python
https://opensource.com/article/18/3/loop-better-deeper-look-iteration-python

Itertools in Python 3, By Example
https://realpython.com/python-itertools/