yield

Learn generator functions with yield.

yield

The yield keyword turns a function into a generator. Unlike return, after producing a value the function does not end; it pauses and continues from where it left off on the next call.

Example: def count_up():\n yield 1\n yield 2\n yield 3. The call for v in count_up(): produces 1, 2, 3 in order. Each yield gives a value and the function pauses. Generators are ideal for producing large data lazily; the whole list is not loaded into memory.

Lazy production

Generators work lazily: a value is not produced until requested. The next(g) call advances to the next yield. The for loop does this automatically.

This property is useful for infinite sequences or very large data. Example: def fib():\n a, b = 0, 1\n while True:\n yield a\n a, b = b, a + b. This generator never ends; but you can safely take the first 10 terms with islice(fib(), 10).

Exercise Write the count_up generator

Define the function def count_up():. In the body include yield 1, yield 2 and yield 3. Then loop with for v in count_up(): and print each value with print(v).

Show example solution

# Write the count_up generator and print values
def count_up():
    yield 1
    yield 2
    yield 3

for v in count_up():
    print(v)

Test yourself

How does yield differ from return?
- It runs faster
- It does not end the function, it pauses
- It only returns numbers
- It is used inside classes
Show answer

It does not end the function, it pauses — yield produces a value and pauses.

Complete the yield line

def count_up():
    ____ 1
    yield 2
    yield 3

Show answer

def count_up():
    yield 1
    yield 2
    yield 3

Match the yield parts

yield

Produce value
next(g)

Next value
for v in g

Auto iteration
pause

Pause

Next lesson: Generator object

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