Python Iterators

An iterator is an object that contains a countable number of values. In Python, an iterator is an object which implements the iterator protocol, consisting of the methods __iter__() and __next__().

Creating an Iterator

You can create an iterator from any iterable object, such as a list, tuple, or string, by using the iter() function.

In this example, my_list is an iterable, and my_iterator is an iterator created from my_list. The next() function is used to get the next item from the iterator.

my_list = [1, 2, 3, 4, 5]
my_iterator = iter(my_list)

print(next(my_iterator))  # Output: 1
print(next(my_iterator))  # Output: 2

Using Iterators in a Loop

Iterators are often used in loops to iterate through elements of a collection.

You can use a for loop to automatically handle the iteration process. This loop will continue to print each item from the iterator until all items have been exhausted.

for item in my_iterator:
    print(item)

Creating a Custom Iterator

You can create a custom iterator by defining a class that implements the __iter__() and __next__() methods.

In this example, MyNumbers is a custom iterator that returns numbers from 1 to 5. The __iter__() method initializes the iterator and the __next__() method returns the next value.

class MyNumbers:
    def __iter__(self):
        self.a = 1
        return self

    def __next__(self):
        if self.a <= 5:
            x = self.a
            self.a += 1
            return x
        else:
            raise StopIteration

my_numbers = MyNumbers()
my_iterator = iter(my_numbers)

for number in my_iterator:
    print(number)

Python Iterators Example Code

This program shows how to create an iterator from a list, use it in a loop, and create a custom iterator.

# Creating an iterator from a list
my_list = [1, 2, 3, 4, 5]
my_iterator = iter(my_list)

print(next(my_iterator))  # Output: 1
print(next(my_iterator))  # Output: 2

# Using an iterator in a loop
for item in my_iterator:
    print(item)

# Creating a custom iterator
class MyNumbers:
    def __iter__(self):
        self.a = 1
        return self

    def __next__(self):
        if self.a <= 5:
            x = self.a
            self.a += 1
            return x
        else:
            raise StopIteration

my_numbers = MyNumbers()
my_iterator = iter(my_numbers)

for number in my_iterator:
    print(number)

Python Labs