Sending values into a generator

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Accepted Answer

yield is an expression, not just a statement - it can return a value sent from outside. x = yield produces x = None normally, but x = generator.send(10) makes x = 10 inside the generator. This two-way communication is the basis of coroutines in Python and how async/await is implemented under the hood. The first call must be send(None) or next() to advance to the first yield before you can send a non-None value.