`iter()` Function in Python [ English ]

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1. Introduction

The iter() function in Python is a built-in function used to convert an iterable object into an iterator. An iterator is an object that allows elements to be accessed one at a time, making it useful for sequential processing of data.

Common iterable objects include lists, tuples, strings, sets, and dictionaries. The iter() function enables us to traverse these objects step by step using the next() function.

2. Syntax

iter(object, sentinel)

Parameters

1. object An iterable object (such as a list, tuple, or string).

2. sentinel (optional) A value that signals the end of iteration when using a callable.

3. Return Value

• Returns an iterator object that can be used to access elements one by one.

4. Basic Example

numbers = [10, 20, 30]

it = iter(numbers)

print(next(it))
print(next(it))
print(next(it))

Output

10
20
30

Explanation

• iter(numbers) converts the list into an iterator.
• next(it) retrieves elements one by one.

5. Example with a String

text = "Python"

it = iter(text)

print(next(it))
print(next(it))

Output

P
y

Explanation

• Each call to next() returns the next character.

6. Using iter() in a Loop

numbers = [1, 2, 3]

it = iter(numbers)

for item in it:
    print(item)

Output

1
2
3

Explanation

• The iterator is used to traverse the list using a loop.

7. Handling End of Iteration

numbers = [1, 2]

it = iter(numbers)

while True:
    try:
        print(next(it))
    except StopIteration:
        break

Output

1
2

Explanation

• When no elements are left, Python raises a StopIteration exception.

8. Using iter() with Sentinel Value

import random

def get_number():
    return random.randint(1, 5)

for num in iter(get_number, 3):
    print(num)

Explanation

• The function keeps generating numbers.
• Iteration stops when the value 3 is returned.

9. Iterable vs Iterator

Example:

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

• numbers → iterable
• it → iterator

10. Summary

• iter() is a built-in Python function used to create an iterator from an iterable object.
• It allows elements to be accessed one at a time.
• It is commonly used with the next() function.
• Iteration ends with a StopIteration exception.
• It can also be used with a sentinel value for controlled iteration.