How is the iteration mechanism over objects implemented in Python?

In Python, the iteration mechanism is implemented through the iterator protocol, which includes two methods: __iter__() and __next__().

• An object is considered iterable if it has a __iter__() method that returns an iterator.
• An iterator is an object with a __next__() method that returns the next element in the sequence each time it is called, or raises a StopIteration exception when the elements are exhausted.

Example of implementing a custom iterator:

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 for loop automatically calls __iter__() and then repeatedly calls __next__() to get the elements.