Python next() function

Summary: in this tutorial, you’ll learn how to use the Python next() function and how to use it to retrieve the next item from an iterator.

Introduction to the Python next() function #

An iterator is an object that implements the iterator protocol which consists of two methods:

• __iter__() method that returns the iterator object itself.
• __next__() method that returns the next item. If all items have been returned, the __next__() method raises a StopIteration exception.

The next() function get the next item from an iterator by calling its __next__() method.

Here’s the syntax of the next() function:

next(iterator[, default])Code language: Python (python)

The next() function has two parameters:

• iterator – this required argument specifies an iterator from which you want to retrieve the next item.
• default – this is an optional argument. The next() function returns the default if the iterator is exhausted; otherwise, it’ll raise a StopIteration exception.

Python next() function examples #

Let’s take some examples of using the next() function.

1) Using Python next() function with an iterator example #

The following example defines an iterator that returns a number of random numbers between min and max and uses the next() function to get the next random number from the iterator:

from random import randint


def random_seq(min, max, size):
    for _ in range(0, size):
        yield randint(min, max)


random_numbers = random_seq(1, 100, 3)

r = next(random_numbers)
print(r)

r = next(random_numbers)
print(r)

r = next(random_numbers)
print(r)Code language: Python (python)

How it works.

First, import the randint() function from the built-in random module:

from random import randintCode language: Python (python)

Second, define a generator that returns a number of random integers between min and max:

def random_seq(min, max, size):
    for _ in range(0, size):
        yield randint(min, max)Code language: Python (python)

Third, call the random_seq function:

random_numbers = random_seq(1, 100, 3)Code language: Python (python)

The random_numbers is a generator which is also an iterator.

Fourth, call the next() function three times to get the next item from the random_numbers iterator:

r = next(random_numbers)
print(r)

r = next(random_numbers)
print(r)

r = next(random_numbers)
print(r)Code language: Python (python)

It should display three random numbers between 1 and 100.

If you call the next() function one more time, you’ll get a StopIteration exception:

r = next(random_numbers) # StopIterationCode language: Python (python)

However, if you use a default value, the next() function will return that value instead of raising the StopIteration exception:

r = next(random_numbers, None)
print(r)  # NoneCode language: Python (python)

2) Using Python next() function to skip heading when reading a csv file #

The following example uses the built-in csv module to read the country.csv file with the following information:

import csv

with open('country.csv', encoding='utf8') as f:
    csv_reader = csv.reader(f)

    # skip the header
    next(csv_reader)

    # iterate over the data line
    for line in csv_reader:
        print(line)Code language: Python (python)

How it works.

First, import the csv module:

import csvCode language: Python (python)

Second, open the country.csv file and return the reader object from the csv.reader() function. The reader object is an iterator.

with open('country.csv', encoding='utf8') as f:
    csv_reader = csv.reader(f)
    #... Code language: Python (python)

Third, call the next() function to retrieve the header from the csv_reader iterator:

next(csv_reader)Code language: Python (python)

Finally, display all the data lines:

for line in csv_reader:
    print(line)Code language: Python (python)

Summary #

• Use the Python next() function to get the next item from an iterator.