What does the yield keyword do in Python

Understand the use of yield keyword with examples.

The yield keyword in Python is used exclusively with generators to return values on iteration. In this article, we will explore yield in terms of its use and purpose with examples.

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Purpose of yield¶

Generators are function like structures in Python, except on calling a generator we do not receive the output, but instead a generator object is returned. The return keyword used in a normal function is analogous to yield in a generator.

The generator returns an object only on iteration or when used with next(). When an object is yielded the state of the generator is saved in memory.

Examples of yield¶

Create a sequence from 0 to 9

Using a function¶

def create_sequence_func():
    return [n for n in range(10)]

print(create_sequence_func())

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9]

Using a generator¶

def create_sequence_gen():
    for n in range(10):
        yield n

print(create_sequence_gen())

Printing this will print only the generator object:

<generator object create_sequence_gen at 0x7fd2806d80f8>

But when iterating over a generator we can access items like with a normal sequence:

for n in create_sequence_gen():
    print(n)

Output:

0
1
2
3
4
5
6
7
8
9

We could also convert a generator back to a list:

print(list(create_sequence_gen()))

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9]

Or we can create a generator object and access items with next():

gen = create_sequence_gen()
print(next(gen))
print(next(gen))

Output:

1
2