Python Iterators

🐍 Python Iterators

An iterator is an object that allows you to iterate (loop) through a sequence of values—such as strings, lists, tuples, etc.

Iterators are used when you want to process items one at a time.

✅ What Makes an Object Iterable?

An object is iterable if:

It can return items one by one
It contains the method __iter__()

Examples: list, tuple, string, set, dict

What is an Iterator?

An iterator is an object that implements:

Method	Purpose
`__iter__()`	Returns the iterator object
`__next__()`	Returns the next value

Example: Using Iterator Manually

If you call next() again, you get:

Using Iterators in Loops

Instead of writing next() manually, Python automatically uses iterators inside loops:

String as an Iterator

🧠 Creating Your Own Iterator Class

You can create a custom iterator by defining the two required methods:

Output:

Infinite Iterators

You can create infinite iterators (no stopping condition).
Use carefully to avoid infinite loops.

Iterator vs Iterable (Quick Difference)

Feature	Iterable	Iterator
Can be looped	✅ Yes	✅ Yes
Needs `__iter__()`	✅ Yes	✅ Yes
Needs `__next__()`	❌ No	✅ Yes
Examples	`list`, `tuple`, `str`	`iter(list)`

Why Use Iterators?

✔ Saves memory (values created one at a time)
✔ Useful for large datasets
✔ Used in loops, generators, and file reading

🧠 Real Example: Reading Files with Iterator

Python reads one line at a time → efficient for large files.

📌 Summary

Iterators let you loop through values one at a time.
Any object with __iter__() is iterable.
Iterator object must also have __next__().
Best used for large data and memory-efficient looping.

🚀 Practice Exercises

Create an iterator that prints numbers from 1 to 20.
Make a countdown iterator starting from 10 to 1.
Create an iterator that returns even numbers only.
Convert a string into an iterator and print characters using next().

Python Iterators