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What does the built-in next() function's optional default argument do?

Beginner

Answer

next(iterator, default) returns default instead of raising StopIteration when the iterator is exhausted. This avoids needing a try/except block when you just want a fallback value for an empty or finished iterator.
empty = iter([])
print(next(empty, 'no items'))  # 'no items' instead of StopIteration
Real-world example A search function uses next((x for x in items if x.match), None) to get the first matching item or None without writing an explicit loop.

Common follow-ups: How does this pattern replace a manual for-loop with early return?;Is there a performance cost to the default check?

Exception Handling;Comprehensions & Generators
All 15 Iterators & the Iterator Protocol questions