Introduction to Python Iterators

Python Iterators

An iterator is an object that implements the iterator protocol, which consists of the __iter__() and __next__() methods.

Iterators are used to iterate over a collection of elements or to generate a sequence of values on the fly.

To create an iterator in Python, you need to define a class that implements the iterator protocol.

As an example:

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

# Creating an iterator using iter()
my_iter = iter(my_list)

# Iterating over the elements using next()
print(next(my_iter))  # Output: 1
print(next(my_iter))  # Output: 2
print(next(my_iter))  # Output: 3
print(next(my_iter))  # Output: 4
print(next(my_iter))  # Output: 5

In this example:

• We have a list called my_list containing some elements.
• We create an iterator object my_iter using the iter() function, passing in my_list as the argument.
• The iter() function converts the list into an iterator.

• We then use the next() function to retrieve the next element from the iterator.
• Each call to next(my_iter) returns the next element in the sequence.
• In this case, we call next() five times to retrieve all the elements from the iterator and print them.
• The output will be the elements of the list printed one by one: 1, 2, 3, 4, 5.

Iterable

An iterable is an object that can be looped over or iterated upon.

It is a more general concept and includes any object that can return an iterator. Iterables can be used directly in a for loop or passed to functions that expect iterables.

As an example:

my_list = [1, 2, 3]
for item in my_list:
    print(item)

In the above example:

• my_list is an iterable that can be iterated over using a for loop.
• The for loop implicitly creates an iterator from the iterable and retrieves elements one by one.

Iterator

An iterator is an object that represents a stream of data and provides a way to access the elements of the stream sequentially.

It implements the iterator protocol, which requires the object to have the __iter__() method that returns the iterator object itself and the __next__() method that retrieves the next element.

Iterators maintain state while iterating over the elements and can remember the position of the last accessed element.

As an example:

my_iter = iter(my_list)
print(next(my_iter))  # Output: 1
print(next(my_iter))  # Output: 2
print(next(my_iter))  # Output: 3

In this example:

• my_iter is an iterator created using the iter() function.
• The next() function is used to retrieve elements from the iterator sequentially.