In Python what are iterators?

An iterator in Python is an object that represents a stream of data. It implements the Python Iterator Protocol, which consists of two core magic methods:

1. __iter__(): Returns the iterator object itself.
2. __next__(): Returns the next item from the sequence. When no elements remain, it raises the StopIteration exception.

### Custom Iterator Example:

class CountUpTo:
    def __init__(self, max_value):
        self.max_value = max_value
        self.current = 1

    def __iter__(self):
        return self

    def __next__(self):
        if self.current <= self.max_value:
            val = self.current
            self.current += 1
            return val
        raise StopIteration

counter = CountUpTo(3)
for num in counter:
    print(num)  # Prints 1, 2, 3

### Iterable vs Iterator:

• An Iterable is any object that can return an iterator via iter(obj) (e.g. lists, tuples, dicts, strings).
• An Iterator is the stateful helper that actually produces values one at a time via next(it).