[Python] Use next() Function To Read The Iterator Elements

Last Updated on 2021-09-20 by Clay

Recently, when I reading the source code of a Python project, I saw they used next() function to take the iterator elements. At first I didn’t know how to use the function, so I decided to study the use and record it.

The following is simple record of the purpose of the next() function and the iter() function that is often used together.

How to use next() function

The next() function returns the next element of the “iterator“, so if we have many elements stored in a List or Tuple and want to use the next() function to read out, we need to use the iter() function to convert it into an iterator.

# coding: utf-8


def main():
    data = [1, 2, 3, 4, 5]
    data = iter(data)

    print(next(data))
    print(next(data))
    print(next(data))


if __name__ == '__main__':
    main()

Output:

1
2
3

As you can see, next() function will read out the elements.

If we set a specified parameter for next(), it will become the default null element.

# coding: utf-8


def main():
    data = [1, 2, 3, 4, 5]
    data = iter(data)

    for _ in range(10):
        print(next(data, 777))


if __name__ == '__main__':
    main()

Output:

1
2
3
4
5
777
777
777
777
777

Just like the above program. If the default value is not specified and an empty object is read, an error message StopIteration will be thrown.

References

• https://www.programiz.com/python-programming/methods/built-in/next
• https://www.w3schools.com/python/ref_func_next.asp
• https://www.geeksforgeeks.org/python-next-method/

Read More

• [Python] Use map() function to iterate the parameter list to a function
• [Python] Use enumerate() function to output index and element at the same time
• [Python] How to use filter() function