How to Use itertools.permutations in Python: Simple Guide

Use itertools.permutations(iterable, r) to get all possible ordered arrangements of length r from the iterable. If r is omitted, it defaults to the length of the iterable, producing full-length permutations.

Syntax

The itertools.permutations function has this syntax:

• itertools.permutations(iterable, r=None)

Here:

• iterable: any sequence like a list, string, or tuple to permute.
• r: optional length of each permutation; if not given, it uses the full length of the iterable.

The function returns an iterator of tuples, each tuple is one permutation.

python

import itertools

perms = itertools.permutations(['a', 'b', 'c'], 2)
for p in perms:
    print(p)

Output

('a', 'b')
('a', 'c')
('b', 'a')
('b', 'c')
('c', 'a')
('c', 'b')

Example

This example shows how to get all permutations of the letters in the word "dog" with length 3 (full length). It prints each permutation as a string.

python

import itertools

word = 'dog'
permutations = itertools.permutations(word)

for p in permutations:
    print(''.join(p))

Output

dog
dgo
god
gdo
odg
god

Common Pitfalls

Some common mistakes when using itertools.permutations:

• Forgetting that the result is an iterator, so you can only loop once unless you convert it to a list.
• Not specifying r when you want shorter permutations, which defaults to full length.
• Trying to modify the tuples returned (they are immutable).

Example of a wrong approach and the fix:

python

# Wrong: trying to reuse iterator
import itertools
perms = itertools.permutations([1, 2, 3])
print(list(perms))  # works first time
print(list(perms))  # prints [] because iterator is exhausted

# Right: convert to list once
perms = list(itertools.permutations([1, 2, 3]))
print(perms)
print(perms)

Output

[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]
[]
[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]
[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]

Quick Reference

Summary tips for using itertools.permutations:

• Use permutations(iterable, r) to get ordered arrangements of length r.
• Result is an iterator of tuples; convert to list if you need to reuse.
• Tuples are immutable; convert to list if you want to modify.
• Works with any iterable: strings, lists, tuples.

Key Takeaways

Use itertools.permutations to generate all ordered arrangements of elements from an iterable.

The second argument r controls the length of each permutation; it defaults to the iterable's length.

The function returns an iterator of tuples, so convert to list to reuse or inspect multiple times.

Tuples returned are immutable; convert to list if you need to change elements.

Works with any iterable like strings, lists, or tuples.