The next function

The next() built-in is a convenient wrapper which can be used to receive a value from any iterator (including a generator iterator) and to provide a default value in case the iterator is exhausted.

def nums():
    yield 1
    yield 2
    yield 3
generator = nums()

next(generator, None)  # 1
next(generator, None)  # 2
next(generator, None)  # 3
next(generator, None)  # None
next(generator, None)  # None
# ...

The syntax is next(iterator[, default]). If iterator ends and a default value was passed, it is returned. If no default was provided, StopIteration is raised.