How to Use itertools.cycle in Python: Simple Guide

Use itertools.cycle(iterable) to create an iterator that repeats the elements of iterable endlessly. It cycles through the items one by one and starts over when it reaches the end.

Syntax

The syntax for itertools.cycle is simple:

• itertools.cycle(iterable): Takes any iterable (like a list, tuple, or string).
• Returns an iterator that repeats the elements of the iterable forever.

python

import itertools

cycler = itertools.cycle(['A', 'B', 'C'])

Example

This example shows how to use itertools.cycle to print the first 10 elements cycling through a list of letters.

python

import itertools

cycler = itertools.cycle(['A', 'B', 'C'])

for _ in range(10):
    print(next(cycler), end=' ')

Output

A B C A B C A B C A 

Common Pitfalls

One common mistake is to forget that cycle never ends on its own. If you use it in a loop without a stopping condition, your program will run forever.

Also, if the original iterable is empty, cycle will raise StopIteration immediately when you try to get the next item.

python

import itertools

# Wrong: infinite loop without break
# cycler = itertools.cycle([1, 2, 3])
# while True:
#     print(next(cycler))  # This will never stop

# Right: use a limit
cycler = itertools.cycle([1, 2, 3])
for _ in range(6):
    print(next(cycler), end=' ')

Output

1 2 3 1 2 3 

Quick Reference

Function	Description
itertools.cycle(iterable)	Creates an iterator that repeats elements of iterable endlessly
next(iterator)	Gets the next element from the cycle
Use with a loop and a limit	Avoid infinite loops by controlling iterations

Key Takeaways

Use itertools.cycle to repeat elements endlessly from any iterable.

Always control the number of iterations to avoid infinite loops.

cycle raises StopIteration immediately if the iterable is empty.

Use next() to get the next item from the cycle iterator.

cycle is useful for repeating patterns without manually resetting.