Python's next() Function

Python's next() function lets you fetch the succeeding element from an iterator. The syntax is:

next(object, default)

The function takes two parameters:

• The first parameter (object) is the iterator object. This is mandatory.
• The second parameter (default) is the message that would be displayed in place of a StopIteration exception. This one's optional.

The function retrieves items from the iterator one by one.

If there aren't any more elements, it triggers a StopIteration exception.

Here's a hands-on example.

Let's start by creating an iterator.

>>> my_iterator = iter([1, 2, 3])

Next, fetch the first element.

>>> next(my_iterator)

1

Fetch the second element.

>>> next(my_iterator)

2

Fetch the third element.

>>> next(my_iterator)

2

Now, if you try to fetch an additional element, the next() function raises a StopIteration exception, since there are no more elements left to return.

>>> next(my_iterator)

Traceback (most recent call last):
StopIteration

If desired, you can customize this final message by providing a string as the second argument for the next function.

>>> my_iterator = iter([1, 2, 3])
>>> next(my_iterator, "End" )
1
>>> next(my_iterator, "End" )
2
>>> next(my_iterator, "End" )
3
>>> next(my_iterator, "End" )
End

In this case, Python doesn't raise the StopIteration exception but instead shows the alphanumeric value "End" that you've specified.