116 – Send data into generators

Generators have a method send that you can use to send data into the generator. Inside the generator, that data comes from the expression yield, that evaluates to the value that was sent into the generator.

The example below shows a generator that produces consecutive integers. However, if you send an integer into the generator, you’ll skip ahead that many integers:

def count():
    at = 0
    while True:
        skip = yield at
        if skip is not None:
            at += skip
        else:
            at += 1

Here’s an example usage:

counter = count()
print(next(counter))  # 0
print(next(counter))  # 1

print(counter.send(5))  # 6

print(next(counter))  # 7

Note how the return value of the method send is the next value produced by the generator.

When you use the built-in next to fetch the next value the result of the yield is None, because no value was sent to the generator.