Context managers & yield as a doorway
P29.iterators-generators.02 · Audience: guest, it-ml, language-pro · Prerequisites: Iterators & generators
with blocks and async/await look unrelated — but both stand on the same
mechanism you met in the last module: a frame suspended at yield. This
module closes the pillar by turning a generator into a context manager, then
opening the door that leads to coroutines and P33.
ⓘ Concept: The context-manager protocol
with open(path) as f: calls __enter__ on entry and __exit__ on the way out — always, success or exception. That pairing (acquire/release, begin/commit-or-rollback, lock/unlock) is the whole protocol: two methods and a guarantee.Why it matters — Files, locks, database transactions — anything with a must-run cleanup belongs in a with block, because __exit__ runs even when the body raises.
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🎓 Practice ladder
2 graded rungs · ~18 minYour turn: build a rollback transaction() guard with
@contextmanager, then close the pillar with the interview
question that links yield to coroutines.
Rung 1 — a transaction guard with @contextmanager
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Interview rung — yield as a doorway to coroutines (free-form)
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That completes Functions, Decorators & Generators: functions as values,
wrappers as design, iteration as a protocol — and yield left standing as
the doorway P33 walks through.
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