Generator functions and yield

A function containing yield returns a generator when called. Its body runs as values are requested, pausing after each yield.

Worked example

def squares(limit):
    for number in range(limit):
        yield number * number

items = squares(4)
print(next(items))
print(list(items))

0
[1, 4, 9]

Why this works

next requests the first square. list then consumes the remaining three values. The generator does not reset after list consumes it.

Another case

def count():
    yield 1
    yield 2
print(sum(count()))

3

Practice

Predict list(squares(3)) using a new generator.

Try another case

items = squares(2); print(list(items)); print(list(items)). What prints?