What is the purpose of the __next__ method in Python iterators?

The __next__ method in Python iterators is designed to retrieve the next element in a sequence. When next() is called on an iterator, it invokes its __next__ method, which returns the next item. If there are no more items, the method should raise a StopIteration exception to signal the end of iteration.

Example of a simple iterator implementation:

class CountUpTo:
    def __init__(self, max):
        self.max = max
        self.current = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.current >= self.max:
            raise StopIteration
        self.current += 1
        return self.current

counter = CountUpTo(3)
for number in counter:
    print(number)  # Will output 1, 2, 3