Generators

Why this matters

Generators power itertools, asyncio's original coroutine model, Django QuerySet iteration, and every streaming ETL job. They're the reason you can process a 50GB log file on a laptop — and a common interview probe for memory awareness.

Common pitfalls

• Iterating a generator twice — it's exhausted after the first pass; wrap in list() or rebuild if you need reuse.
• Confusing yield with return — return in a generator raises StopIteration with the value, not a plain result.
• Building a generator when you need len() or indexing — you'll get TypeError; use a list or itertools.tee.