Python iter(): Create an Iterator from an Iterable

The iter() function converts an iterable (like a list, tuple, or string) into an iterator, allowing elements to be accessed one at a time. It’s useful for looping through data, working with custom objects, and controlling iteration manually.

Example

numbers = [1, 2, 3]
iterator = iter(numbers)

print(next(iterator))  # Output: 1
print(next(iterator))  # Output: 2
print(next(iterator))  # Output: 3

The next() function fetches the next item from the iterator.

Syntax

iter(iterable)

• iterable → A list, tuple, string, or any object that supports iteration.
• Returns → An iterator object.

1. Iterating Over Strings with iter()

word = "Python"
iterator = iter(word)

print(next(iterator))  # Output: P
print(next(iterator))  # Output: y

Great for processing characters one by one.

2. Using iter() in a Loop

Instead of next(), use for loops to automatically iterate.

numbers = [10, 20, 30]
iterator = iter(numbers)

for num in iterator:
    print(num)

Loops automatically call next() until all items are exhausted.

3. Creating an Iterator from a Custom Object

Define an iterable class using iter() and next().

class Counter:
    def __init__(self, start, end):
        self.current = start
        self.end = end

    def __iter__(self):
        return self

    def __next__(self):
        if self.current > self.end:
            raise StopIteration
        self.current += 1
        return self.current - 1

counter = Counter(1, 3)

for num in counter:
    print(num)

Output:

1  
2  
3

Useful for custom iteration logic.

4. Using iter() with a Sentinel Value

Convert a function into an iterator until a stop value is reached.

import random

rand_iterator = iter(lambda: random.randint(1, 10), 5)

for num in rand_iterator:
    print(num)  # Stops when 5 is generated

This is great for reading files or streams.

Key Notes

• ✔ Creates an iterator from any iterable.
• ✔ Use next() to access items manually.
• ✔ Loops automatically call next() for you.
• ✔ Can define custom objects as iterators.

By using iter(), you can process data efficiently, control iteration, and create reusable iterators. 🚀