What is the difference between an iterable and an iterator?

Question presented to candidate: "People use 'iterable' and 'iterator' as if they meant the same thing. What exactly is the difference in Python? If I give you a list and a generator, which is which, and why can I loop over the list twice but not the generator?"

What a strong answer should cover:

• An iterable is anything iter() can turn into an iterator: it defines __iter__ (or the older __getitem__ sequence protocol). An iterator is the object that actually produces values: it defines __next__, plus an __iter__ that returns itself
• next() on an exhausted iterator raises StopIteration; iterators are single-pass and never rewind
• A container such as a list hands out a new, independent iterator on every iter() call, so it can be looped over many times; a generator, map, zip, enumerate or a file object is its own iterator, so it is consumed once
• Every iterator is iterable, but not every iterable is an iterator (isinstance(x, Iterator) vs Iterable, and why iter(x) is x is the quick test)
• Practical consequences: in, any(), sum() partially or fully consume an iterator; the right design is an iterable class whose __iter__ returns a fresh iterator (often a generator)
• The reliable "is it iterable?" check is calling iter() and catching TypeError, because collections.abc.Iterable misses __getitem__-only classes

Code / implementation expected: Optional — a small class pair (container plus iterator) or a demonstration that list(gen) is empty the second time.