Python iter() Function

L = ['C++', 'Java', 'Python']

for i in iter(L):
    print(i)

The iter() function  is used to create an iterator that iterates through the elements of an iterable object. 

iter(iterable, sentinel[optional])

The required iterable argument represents the object that is to be iterated over. It can be any iterable object such as a list, tuple, string, or custom object that implements the iteration protocol. 

The optional sentinel parameter is used to specify a sentinel value that, when returned by the iterator's __next__() method, will indicate the end of iteration.

L = [1, 2, 3, 4, 5]

for i in iter(L):
    print(i)

iter with callable objects

When the iter() function is called with a callable object that implements the iterator protocol, it creates an iterator using that object. The iterator is responsible for generating values by repeatedly calling the __next__() method of the callable object until a specific condition is met (such as reaching the end of a sequence or encountering a sentinel value).

class Countdown:
    def __init__(self, start):
        self.start = start

    def __iter__(self):
        return self

    def __next__(self):
        if self.start < 0:
            raise StopIteration
        current = self.start
        self.start -= 1
        return current
    __call__ = __next__

countdown_iterator = iter(Countdown(10))
for number in countdown_iterator:
    print(number)