How to Generate Permutations of Length r in Python

Generate all ordered arrangements of length r from a given list of elements using itertools.permutations.

Easy Python 3.9+ Aug 9, 2026 Comprehensions & generators 14 views 0 copies

permutations itertools combinatorics generators

Python code

16 lines

Python 3.9+

from itertools import permutations

def generate_permutations(elements, r):
    """Generate all r-length permutations of the given elements."""
    return list(permutations(elements, r))

if __name__ == "__main__":
    elements = ['A', 'B', 'C']
    r = 2
    result = generate_permutations(elements, r)
    print(f"Elements: {elements}")
    print(f"Length r: {r}")
    print("Permutations:")
    for perm in result:
        print(perm)
    print(f"Total: {len(result)}")

Output

stdout

Elements: ['A', 'B', 'C']
Length r: 2
Permutations:
('A', 'B')
('A', 'C')
('B', 'A')
('B', 'C')
('C', 'A')
('C', 'B')
Total: 6

How it works

The itertools.permutations function returns an iterator that yields tuples of length r containing all possible orderings of the input elements. When r is not specified, it defaults to the length of the iterable, producing full permutations. The list() call consumes the iterator into a list for easy inspection and reuse. Each permutation is a tuple that preserves the order of selection, making this ideal for problems where sequence matters.

Common mistakes

Forgetting that permutations consider order: ('A','B') is different from ('B','A'), unlike combinations.
Using a large `r` with a big input list can produce a huge number of results (n! / (n-r)!), leading to memory issues.
Passing a generator as the first argument to `permutations` works, but be aware it will be consumed once.
Not converting the iterator to a list when you need to access the permutations multiple times.

Variations

Use `itertools.combinations` if order does not matter.
Generate permutations lazily with a loop: `for p in permutations(elements, r):` to avoid memory bloat.

Real-world use cases

Generating all possible ordering schedules for a small set of tasks to find an optimal sequence.
Enumerating candidate passwords of fixed length during a security audit or brute-force test.
Creating all possible arrangements of n items for testing combinatorial logic in unit tests.

How to Generate Permutations of Length r in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Comprehensions & generators

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