Python Iterator

In Python, an iterator is an object that can be iterated or looped upon. It is used to implement the iterator protocol that consists of two methods:

1. __iter__: This method returns the iterator object itself. It is used in for and in statements.

2. __next__: This method returns the next value in the iterator. It raises the StopIteration exception when there are no more items left to return.

Here's an example of creating an iterator for a list in Python:

class MyIterator:
    def __init__(self, my_list):
        self.my_list = my_list
        self.index = 0
        
    def __iter__(self):
        return self
    
    def __next__(self):
        if self.index >= len(self.my_list):
            raise StopIteration
        else:
            result = self.my_list[self.index]
            self.index += 1
            return result
            
my_list = [1, 2, 3, 4, 5]
my_iter = MyIterator(my_list)

for item in my_iter:
    print(item)

Output:

1
2
3
4
5

In the above example, we created a custom iterator MyIterator that takes a list as input. The __init__ method initializes the iterator with the list and the __iter__ method returns the iterator object itself. The __next__ method returns the next value in the iterator, and raises the StopIteration exception when there are no more items left to return.

We then created an instance of MyIterator with a list [1, 2, 3, 4, 5] and looped through it using a for loop. The for loop calls the __iter__ method to get the iterator object and then calls the __next__ method to get the next value in the iterator. This continues until the StopIteration exception is raised.