Iterators

Iterators are objects that allow traversal through all the elements of a collection, regardless of its specific implementation. The iterator protocol requires two methods: __iter__() which returns the iterator object itself, and __next__() which returns the next value in the sequence and raises StopIteration when there are no more items. Many built-in types (lists, tuples, strings, dictionaries, sets) are iterable, meaning they can return an iterator. The iter() function gets an iterator from an iterable, and next() gets the next value from an iterator. Custom iterators are useful when you need complex iteration logic that isn't easily achieved with existing iterables. They allow you to define exactly how iteration should work for your objects. Understanding iterators is fundamental to understanding how Python's for loops work internally and how to make your own objects work with Python's iteration syntax.