Coroutines

Coroutines are extremely powerful constructs that are often confused with generators. Many authors inappropriately describe coroutines as "generators with a bit of extra syntax." This is an easy mistake to make, as, way back in Python 2.5, when coroutines were introduced, they were presented as "we added a send method to the generator syntax." This is further complicated by the fact that when you create a coroutine in Python, the object returned is a generator. The difference is actually a lot more nuanced and will make more sense after you've seen a few examples.

Note

While coroutines in Python are currently tightly coupled to the generator syntax, they are only superficially related to the iterator protocol we have been discussing. The upcoming (as this is published) Python 3.5 release makes coroutines a truly standalone object and will provide a new syntax to work with them.

The other thing to bear in mind is that coroutines are pretty hard to understand. They are not used all...