How to Use Python's next() Builtin with a Default Sentinel Value

A wrapper function that returns the next item from an iterator, or a default sentinel value when the iterator is exhausted.

Easy Python 3.9+ Aug 9, 2026 Functions & basics 14 views 0 copies

next iterator sentinel builtin

Python code

15 lines

Python 3.9+

def get_next_or_default(iterator, default=None):
    """Return the next item from an iterator, or default if exhausted."""
    return next(iterator, default)


if __name__ == "__main__":
    fruits = iter(["apple", "banana", "cherry"])
    
    print(get_next_or_default(fruits))           # apple
    print(get_next_or_default(fruits))           # banana
    print(get_next_or_default(fruits))           # cherry
    print(get_next_or_default(fruits, "none"))  # none (iterator exhausted)
    
    empty_list = iter([])
    print(get_next_or_default(empty_list, "empty"))  # empty

Output

stdout

apple
banana
cherry
none
empty

How it works

The next() builtin in Python accepts an optional second argument that is returned when the iterator is exhausted. By passing a default value like None or a custom sentinel, you avoid raising the StopIteration exception. This wrapper function encapsulates that pattern, making it reusable and explicit at the call site. The default parameter defaults to None, but callers can override it with any value, such as a string or a custom object.

Common mistakes

Forgetting that `next()` without a default raises `StopIteration` when the iterator is empty
Passing a mutable object like a list as the default, which gets shared across calls
Confusing the iterator itself with the sequence — `iter()` must be called before passing to `next()`

Variations

Use a sentinel object like `object()` to distinguish 'no more items' from a meaningful `None` value
Loop directly with `for item in iterator` to avoid manual `next()` calls entirely

Real-world use cases

Streaming paginated API responses where a default value handles the final empty page.
Processing command-line arguments or config tokens in a loop that needs a fallback.
Iterating over socket or file chunks when the stream ends unexpectedly.

How to Use Python's next() Builtin with a Default Sentinel Value

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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