Lesson 13 — Generators

Lazy sequences

A function with yield is a generator. Each call to next() runs it until the next yield, hands out that value, and pauses right there. The next call continues from the same spot, so local variables keep their values.

def countdown(n):
    while n > 0:
        yield n
        n -= 1

Why it matters: generators produce values one at a time, so they handle huge or even endless sequences without filling memory.