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Python Concurrency for Senior Engineering Interviews

Yield From

Explore how the yield from syntax in Python enhances asynchronous programming by simplifying delegation to subgenerators and enabling transparent communication using send, throw, and close methods. Understand practical examples and the advantages of yield from over manual generator handling.

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Yield From

The yield from syntax was introduced in PEP-380. The stated motivation for introducing the syntax is to enable refactoring of existing code that utilizes yield easier. The yield from syntax is as follows:

yield from <expr>

The expression must be an iterable from which an iterator is extracted. Let's understand the problem that yield from solves. Consider the following snippet of code:

def nested_generator():
    i = 0
    while i < 5:
        i += 1
        yield i


def outer_generator():
    nested_gen = nested_generator()

    for item in nested_gen:
        yield item

if __name__ == "__main__":

    gen = outer_generator()

    for item in gen:
        print(item)

The above code has two generator functions. The outer_generator() calls the nested_generator() in a loop and returns values from the inner generator to the main script. You can run the code below and examine the output.

Python 3.5
def nested_generator():
    i = 0
    while i < 5:
        i += 1
        yield i
def outer_generator():
    nested_gen = nested_generator()
    for item in nested_gen:
        yield item
if __name__ == "__main__":
    gen = outer_generator()
    for item in gen:
        print(item)

We can refactor the above code and remove the for loop in the outer_generator() as follows, with the same output.

def nested_generator():
    i = 0
    while i < 5:
        i += 1
        yield i

def outer_generator_with_yield_from():
    nested_gen =
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