Python | Iterators

Python | Iterators

In the domain of programming, data manipulation is a fundamental skill, and Python provides an elegant toolkit to overcome the complexities of working with datasets. Among its collection of features, iterators stand out as powerful tools that streamline the process of traversing through data collections. In this article, we’ll begin on a journey to uncover the beauty and functionality of iterators in Python along with examples.

At its core, iteration involves looping through a sequence of items and performing some operation on each item. Whether you’re dealing with lists, strings, dictionaries, or custom objects, iterators are the backbone of this process.

Introducing Iterators:

An iterator in Python is an object designed to facilitate sequential iteration over a collection of items. It stick to the Iterator Protocol, a set of methods that equip it with the capability to generate elements one at a time. Iterator also keep track of current iteration/element.

The two key methods of an iterator are:

  • __iter__(): This method returns the iterator object itself, enabling it to be used in a for loop or other iteration contexts.
  • __next__(): This method fetches the next item in the sequence. When there are no more items to be returned, it raises the StopIteration exception.

Creating Custom Iterators:

To truly grasp the power of iterators, let’s create a custom iterator for a hypothetical book collection. This example will illustrate how you can traverse through different attributes of each book.

Define the class along with 3 special methods
1 : __init__()
2 : __iter__()
3 : __next__()
class BookIterator:
    def __init__(self, books):
        self.books = books
        self.index = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.index < len(self.books):
            current_book = self.books[self.index]
            self.index += 1
            return f"Title: {current_book['title']}, Author: {current_book['author']}"
            raise StopIteration

# creating the list of dictionaries
books_collection = [
    {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald"},
    {"title": "To Kill a Mockingbird", "author": "Harper Lee"},
    {"title": "1984", "author": "George Orwell"}

# creating object of BookIterator class
book_iterator1 = BookIterator(books_collection)

print("Iterate using for loop: \n")
for book in book_iterator1:


# creating object of BookIterator class
book_iterator2 = BookIterator(books_collection)

print("Iterate using next() function and \
__next__() method: \n")



Iterate using for loop: 

Title: The Great Gatsby, Author: F. Scott Fitzgerald
Title: To Kill a Mockingbird, Author: Harper Lee
Title: 1984, Author: George Orwell

Iterate using next() function and __next__() method: 

Title: The Great Gatsby, Author: F. Scott Fitzgerald
Title: To Kill a Mockingbird, Author: Harper Lee
Title: 1984, Author: George Orwell

Built-in Iterators in Action:

Python’s built-in data structures come equipped with default iterators that simplify the process of accessing their elements. Here’s an example using a list:

fruits = ["apple", "banana", "cherry"]

# Using the built-in iterator
# iter() function convert iterable into iterator
fruit_iterator = iter(fruits)

print(next(fruit_iterator))  # Outputs: apple
print(next(fruit_iterator))  # Outputs: banana
print(next(fruit_iterator))  # Outputs: cherry

Advantages of Iterators:

  • Efficient Memory Usage: Iterators work with one item at a time, making them memory-efficient, especially for large datasets.
  • Lazy Evaluation: Elements are fetched as needed, resulting in optimized computation and resource management.
  • Readability and Simplicity: Iterators abstract away complex iteration logic, leading to cleaner and more readable code.
  • Infinite Sequences: Iterators can be employed to generate infinite sequences, which is a hard task with standard data structures.


By understanding iterators and their protocol, you can efficiently navigate through diverse datasets, from lists to custom objects. Whether you’re creating custom iterators or harnessing the power of built-in ones, mastering iterators unlocks the potential to write more efficient, expressive, and Pythonic code.

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