Python next() Function

The next() function returns the next item in an iterator. If the items in the collection are exhausted, Python throws a StopIteration exception.

Syntax

Python

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next(iterator, next = None)

Parameters

Parameter	Description
`iterator`	Required. The iteretor for which the next value should be retrieved
`next`	Optional. If provided, and if the iterator has run out of values, then `next` will be returned .

Example

Python

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myList = ['apples', 'oranges', 'bananas']
myIter = iter(myList)

# first item
item = next(myIter)
print(item)

# second item
item = next(myIter)
print(item)

# third item
item = next(myIter)
print(item)

# the fourth item does not exist in myList
item = next(myIter)
print(item)

Output

apples
oranges
bananas
Traceback (most recent call last):
  File "test.py", line 17, in <module>
    item = next(myIter)
StopIteration

Notes

Typically iteration is handled in a for loop. The advantage of using a for loop is that you don't have to handle the StopIteration exception when the all the items in the collection have been exhausted.

Example

Python

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myList = ['apples', 'oranges', 'bananas']
for item in myList:
    print(item)

Output:

apples
oranges
bananas

You can write write your own iterator by defining the __next__ function, which would normally be implemented as a function in a class.

Example

Python

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class MyIterator:
    n = -1

    def __next__(self):
        if (self.n == 2):
            raise StopIteration
        self.n += 1
        return self.n * 5

myIterator = MyIterator()

# first iteration
item = next(myIterator)
print(item)

# second iteration
item = next(myIterator)
print(item)

# third iteration
item = next(myIterator)
print(item)

# fourth iteration
item = next(myIterator)
print(item)

Output:

0
5
10
Traceback (most recent call last):
  File "test.py", line 25, in <module>
    item = next(myIterator)
  File "test.py", line 6, in __next__
    raise StopIteration
StopIteration