What is the difference between an iterable and an iterator in Python?

Distinguishes sources that can produce iteration from stateful one-pass iterators and explains exhaustion and repeatability.

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TL;DR

An iterable is an object that can produce an iterator, normally through iter(value). A list is iterable and each iteration can obtain a new iterator. An iterator represents the current traversal state: it returns itself from iter and yields the next value from next until it raises StopIteration. Iterators are usually one-pass; after exhaustion, iterating them again produces no values unless a new iterator is created from the original source.

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The iteration protocol, one-pass behavior, lazy APIs, and the ability to avoid accidentally consuming streams.

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Overview
Many Python APIs accept an iterable, while bugs often arise because the supplied value is a one-shot iterator.
An iterable is an object that can produce an iterator, normally through iter(value). A list is iterable and each iteration can obtain a new iterator. An iterator represents the current traversal state: it returns itself from iter and yields the next value from next until it raises StopIteration. Iterators are usually one-pass; after exhaustion, iterating them again produces no values unless a new iterator is created from the original source.
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Calling every iterable an iterator.
Assuming an exhausted generator can be restarted.
Consuming an iterator during logging or validation.
Requiring indexing from an API that accepts any iterable.

What is the difference between an iterable and an iterator in Python?

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