The yield statement doesn't just yield control back to the caller, it also returns a value. This value is passed to the generator function through the next() method. This is how we pass data into generators after they've been created. In this section, we'll address the bidirectional aspect of generators, and how creating feedback loops can produce some lean code.
Some generators are general purpose and used frequently throughout our code. This being the case, does it make sense to constantly create and destroy these generator instances? Or can we reuse them? For instance, consider a sequence that's mainly dependent on initial conditions. Let's say we want to generate a sequence of even numbers. We would start at two, and as we iterate over this generator, the value would be incremented. The next time we want to iterate over even numbers, we would have to create a new generator.
This is kind of wasteful, since all we're doing is resetting a counter...