A generator function is any function that has the yield keyword in its body. When called, generator functions return a generator object that wraps the body of the function.

Generator objects can be consumed like any other iterator. When we call next() on them, execution advances to the next yield statement in the function body, and the yielded value is returned. Finally, when the function body returns, the generator object returns StopIteration.

See example in image: gen_AB() returns a generator that can be iterated over. next() is called on it 3 times in total.