Using the Python next() Function to Retrieve the Next Item from an Iterator

In Python, the built-in next() function returns the next item from an iterator by internally calling the iterator’s __next__() method.

The syntax is next(iterator[, default]), where iterator is any iterable object and the optional default value is returned instead of raising StopIteration when the iterator is exhausted.

Example:

#!/usr/bin/python
# -*- coding: UTF-8 -*-

it = iter([1, 2, 3, 4, 5])
while True:
    try:
        x = next(it)
        print(x)
    except StopIteration:
        break

The loop prints the numbers 1 through 5, and exits cleanly when the iterator is exhausted.

Note that in Python 3 the file object does not implement a next() method; instead the built‑in next() function can be used to retrieve the next line from a file object.

When a default argument is supplied, next() returns that value after the iterator is exhausted instead of raising an exception. For instance:

a = iter('abcd')
print(next(a, 'e'))  # 'a'
print(next(a, 'e'))  # 'b'
print(next(a, 'e'))  # 'c'
print(next(a, 'e'))  # 'd'
print(next(a, 'e'))  # 'e'
print(next(a, 'e'))  # 'e'