What is the difference between an iterable and an iterator?

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These are two roles in the **iteration protocol**:

- An **iterable** is anything you can loop over: it implements `__iter__()`, which returns a fresh **iterator**. Lists, tuples, strings, dicts, sets, files are iterables. They're **reusable** — each `for` loop gets a new iterator.
- An **iterator** implements `__next__()` (and returns *itself* from `__iter__`). It produces items one at a time and raises **`StopIteration`** when exhausted. It's **stateful and single-pass** — once consumed, it's empty.

A `for x in obj:` loop is sugar for: call `iter(obj)` once, then call `next()` repeatedly until `StopIteration`. **Generators are iterators** (so single-use). A list is an iterable but *not* its own iterator — which is why you can loop over the same list many times but a generator only once.

**Interview tip:** the sharp distinction is reusable vs one-shot: `iter(a_list)` gives a *new* iterator each time, but a generator/iterator is consumed after one pass. Be ready to write a class with

What is the difference between an iterable and an iterator?

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