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Python Concurrency for Senior Engineering Interviews

Yield From

This lesson explains the yield from syntax.

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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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