11. Iterators Basics

An iterator is an object that implements the iterator protocol with __iter__() and __next__().

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Example of an Iterator

numbers = [1, 2, 3]
it = iter(numbers)
print(next(it))  # 1
print(next(it))  # 2
print(next(it))  # 3

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Custom Iterator

class CountDown:
    def __init__(self, start):
        self.current = start
    def __iter__(self):
        return self
    def __next__(self):
        if self.current <= 0:
            raise StopIteration
        self.current -= 1
        return self.current

for n in CountDown(3):
    print(n)

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Wrap-Up

• Iterators provide sequential access to elements.
• Use iter() and next() to work with them directly.