Iterables vs iterators - the key distinction

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Accepted Answer

The iterator protocol has two roles. An iterable only needs __iter__, which returns a fresh iterator each time - lists, tuples, and strings are iterables. An iterator must also implement __next__ and typically returns itself from __iter__. This is why you can loop over a list multiple times (each loop calls iter() to get a new iterator) but can only loop over a generator once (it is its own iterator and can't be rewound).