Python 3 Object-Oriented Programming - Third Edition

Closing coroutines and throwing exceptions

Normal generators signal their exit from inside by raising StopIteration. If we chain multiple generators together (for example, by iterating over one generator from inside another), the StopIteration exception will be propagated outward. Eventually, it will hit a for loop that will see the exception and know that it's time to exit the loop.

Even though they use a similar syntax, coroutines don't normally follow the iteration mechanism. Instead of pulling data through one until an exception is encountered, data is usually pushed into it (using send). The entity doing the pushing is normally the one in charge of telling the coroutine when it's finished. It does this by calling the close() method on ...