{"id":3759,"date":"2020-07-30T16:25:13","date_gmt":"2020-07-30T10:55:13","guid":{"rendered":"http:\/\/www.pythonpool.com\/?p=3759"},"modified":"2026-07-13T12:27:39","modified_gmt":"2026-07-13T06:57:39","slug":"python-next","status":"publish","type":"post","link":"https:\/\/www.pythonpool.com\/python-next\/","title":{"rendered":"Python next(): Iterators, Defaults, and StopIteration"},"content":{"rendered":"

Python’s built-in next()<\/code> retrieves one item from an iterator and advances that iterator’s state. Call next(iterator)<\/code> when exhaustion should raise StopIteration<\/code>, or call next(iterator, default)<\/code> when reaching the end is an ordinary outcome. The function is especially useful for reading one value lazily without materializing an entire collection.<\/p>\n

\n\nContents<\/p>\nToggle<\/span>
Quick answer<\/a><\/li>
Get items from an iterator<\/a><\/li>
Handle StopIteration<\/a><\/li>
Provide a default value<\/a><\/li>
Find the first matching item lazily<\/a><\/li>
Understand custom iterators<\/a><\/li>
Choose next or a loop<\/a><\/li>
Use a sentinel when None is valid<\/a><\/li>
Do not reuse an exhausted iterator accidentally<\/a><\/li>
Keep StopIteration inside the iterator boundary<\/a><\/li>
Use next with a file or stream carefully<\/a><\/li>
Keep the first-match predicate pure<\/a><\/li>
Make the exhaustion policy visible<\/a><\/li>
Frequently Asked Questions<\/a>What does next() do in Python?<\/a><\/li>
How do I avoid StopIteration with next()?<\/a><\/li>
How do I find the first matching item?<\/a><\/li>
What is the difference between an iterable and an iterator?<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<\/span>Quick answer<\/span><\/h2>\nTurn an iterable into an iterator with iter()<\/code>, then call next()<\/code>. Use a second argument for a fallback instead of catching StopIteration<\/code> when absence is expected. The official next() documentation<\/a> defines both forms and the iterator protocol.<\/p>\n
next() consumes iterator state; provide a default or handle StopIteration according to whether exhaustion is expected.<\/figcaption><\/figure>\n<\/span>Get items from an iterator<\/span><\/h2>\nA list is iterable but is not itself an iterator. Call iter()<\/code> to create an iterator, then request values one at a time.<\/p>\n
values = [\"first\", \"second\"]\niterator = iter(values)\n\nprint(next(iterator))\nprint(next(iterator))\n<\/code><\/pre>\nEach call advances the same iterator. A second name pointing at that iterator observes the same consumed state; creating a new iterator over the list starts from the beginning.<\/p>\n
<\/span>Handle StopIteration<\/span><\/h2>\nWhen an iterator has no item left, the one-argument form raises StopIteration<\/code>. A for<\/code> loop handles this protocol internally, which is why ordinary loops do not need a manual exception block.<\/p>\n
iterator =

<\/span>Handle StopIteration<\/span><\/h2>\nWhen an iterator has no item left, the one-argument form raises StopIteration<\/code>. A for<\/code> loop handles this protocol internally, which is why ordinary loops do not need a manual exception block.<\/p>\niterator =

<\/span>Handle StopIteration<\/span><\/h2>\n
When an iterator has no item left, the one-argument form raises `StopIteration<\/code>. A for<\/code> loop handles this protocol internally, which is why ordinary loops do not need a manual exception block.<\/p>\n`
`iterator =`