Learn: Iterators and generators

Four notebooks, in order. Each is self-contained but they build on each other — if you work through them in sequence you'll cover the whole topic once.

Notebooks in this section

1. The iteration protocol — what actually happens when you write a for loop. iter(), next(), StopIteration, and why any object with these behaviours fits into Python's iteration machinery.
2. Generator functions — the yield keyword. How generator functions turn sequential code into iterables, pausing between values instead of computing them all at once.
3. Generator expressions and itertools — inline generator syntax ((x*2 for x in xs)) and the standard-library toolkit of iterator combinators.
4. Custom iterators — writing iterator classes when a generator function isn't the right shape. The __iter__/__next__ pair and when you'd reach for them.

After these, the Recipes cover task-focused applications and the Reference has quick lookups for the iterator protocol, generator syntax, and itertools.