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Showing content from https://realpython.com/ref/builtin-functions/next/ below:

Python’s Built-in Functions – Real Python

The built-in next() function retrieves the next item from an iterator, raising a StopIteration exception when the iterator is exhausted:

It can also return a default value if the iterator is exhausted, preventing a StopIteration exception:

next() Signature Arguments Argument Description iterator The iterator from which to retrieve the next item. default The value to return if the iterator is exhausted, preventing the StopIteration exception. Return Value

If the iterator has remaining items, next() returns the next item from the iterator.
If the iterator is exhausted and a default is provided, next() returns the default value.
If the iterator is exhausted and no default is provided, next() raises a StopIteration exception.

next() Examples

With an iterator as an argument:

With a default value:

next() Common Use Cases

The most common use cases for the next() function include:

Manually iterating over an iterator when you need to control the flow of iteration.
Skipping the first item of an iterator, such as a header line in a CSV file.
Providing a default value to avoid StopIteration exceptions when an iterator is exhausted.

next() Real-World Example

A typical use case for next() is reading a CSV file and skipping the header line:

In this example, next(file) skips the first line of the file, which contains the headers. This allows the for loop to process only the data lines.

next() in Custom Classes

You can support next() in your custom classes by implementing the .__next__() method. Say that you want to write an iterator that takes a sequence of numbers, computes the square value of each number, and yields those values on demand. In this case, you can write the following class:

This class takes a sequence of numbers as an argument and makes an iterator of square values. The .__next__() method processes the current number and returns its square value. When there are no more items, .__next__() raises the StopIteration exception.

For additional information on related topics, take a look at the following resources:

Reading and Writing CSV Files in Python (Tutorial)
Python's Magic Methods: Leverage Their Power in Your Classes (Tutorial)
Practical Recipes for Working With Files in Python (Course)
Efficient Iterations With Python Iterators and Iterables (Course)
Iterators and Iterables in Python: Run Efficient Iterations (Quiz)
Reading and Writing CSV Files (Course)
Reading and Writing CSV Files in Python (Quiz)
Python's Magic Methods in Classes (Course)
Python's Magic Methods: Leverage Their Power in Your Classes (Quiz)

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