Useful stackoverflow answers:
- Lazy evaluation, short explanation: https://stackoverflow.com/a/20535379/11217701
- Iterables and generators: https://stackoverflow.com/a/231855/11217701
- Lazy sequences: https://stackoverflow.com/a/30081894/11217701
A Beginner Guide to Python 3 Programming by John Hunt:
- Error and handling - Chapter 24
- Generators - Chapter 30
Good resource but not aimed at beginners: http://getpython3.com/diveintopython3/generators.html