Python next()

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The next(iterator) function is one of Python’s built-in functions—so, you can use it without importing any library. It returns the next value from the iterator you pass as a required first argument. An optional second argument default returns the passed default value in case the iterator doesn’t provide a next value.

Python next()

Syntax:

next(iterator, <default>)

Arguments:

  • iterator – the next element is retrieved from the iterator
  • default (optional) – return value if iterator is exhausted (it doesn’t have a next element)

Related Tutorials:

Python next() – A Simple Guide By Example

Example 1: No Default Value

The following example shows the next() function in action—without using a default value in case the iterator is empty.

users = ['Alice', 'Bob', 'Carl', 'David']

# convert the list to an iterator
users_iterator = iter(users)

x = next(users_iterator)
print(x)
# Output: 'Alice'

x = next(users_iterator)
print(x)
# Output: 'Bob'

x = next(users_iterator)
print(x)
# Output: 'Carl'

x = next(users_iterator)
print(x)
# Output: 'David'

Each time you call next(iterator), the iterator returns the next element in the iterator over the Python list users.

But what happens if you call the next() function once more on the now empty users_iterator object?

x = next(users_iterator)
print(x)
'''
Traceback (most recent call last):
  File "C:\Users\xcent\Desktop\Finxter\Blog\HowToConvertBooleanToStringPython\code.py", line 22, in <module>
    x = next(users_iterator)
StopIteration
'''

Python throws a StopIteration error.

Let’s learn how to fix this!

Example 2: With Default Value

Not providing Python a solution to the problem that the iterator may be empty is a common source of errors! You can fix the errors by passing the optional default argument:

x = next(users_iterator, 42)
print(x)
# 42

Now, you cannot crash the next(...) function anymore! Go ahead and try it…

Interactive Shell

The interactive code shell offers you a way to try your newly gained skill—understanding the next() function. Can you crash the script by changing the function arguments?

Exercise: Run the code in the interactive shell. Now, change the default value & run again!

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