Python iter() method

Python iter() method is a built-in method that allows to create an iterator from an iterable. An iterator is an object that enables us to traverse through a collection of items one element at a time. Let’s start by understanding how iter() works with a simple example.

a = [10, 20, 30, 40]

# Convert the list into an iterator
iterator = iter(a)

# Access elements using next()
print(next(iterator))  
print(next(iterator))  

10
20

Syntax of iter() method

iterator = iter(iterable)

Parameters

• iterable: Any object capable of returning its elements one at a time. Examples include lists, tuples, dictionaries, and strings.

Return Type

• Returns an iterator object that can be used with the next() function or a for loop to access the elements sequentially.

Examples of iter() Method

Using iter() with String

# Convert string to iterator
s = "Python"
iterator = iter(s)

print(next(iterator))  
print(next(iterator))  

P
y

Using iter() with Dictionary

d = {'a': 1, 'b': 2, 'c': 3}
iterator = iter(d)

for key in iterator:
    print(key)  

a
b
c

Using iter() with Callable and Sentinel

# Generate numbers until sentinel value is encountered
import random

iterator = iter(lambda: random.randint(1, 5), 3)
for num in iterator:
    print(num)

5
5

Frequently Asked Questions on iter() Method

Q1: What happens if we call next() on an iterator with no elements left?

Python raises a StopIteration exception, indicating the end of the iterator.

Q2: Can we iterate over an iterator more than once?

No, iterators are exhausted after one full iteration. We must recreate the iterator to iterate again.

Q3: How is iter() different from a loop?

A loop implicitly handles the iteration process while iter() gives us manual control over iteration, element by element.

Q4: Can custom classes use iter()?

Yes, custom classes implementing the __iter__() and __next__() methods can work with iter().

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