What is the role of special double underscore methods in implementing iterators in Python?

In Python, special double underscore methods (so-called dunder methods) play a key role in implementing iterators. To create an iterator in a class, you need to define the following methods:

• __iter__(self): returns the iterator itself (usually self). This method is called when the object is used in a for loop or with the iter() function.
• __next__(self): returns the next element in the sequence. When the end of the sequence is reached, it should raise a StopIteration exception.

Example:

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:
            self.current += 1
            return self.current
        else:
            raise StopIteration

for number in CountUpTo(5):
    print(number)

Thus, the dunder methods __iter__ and __next__ allow objects to behave as iterators, supporting the iteration protocol in Python.