hamming-circle.py

from itertools import combinations, product

def hamming_circle(word, n, alphabet):
    """Create all words of hamming distance `n` in a given alphabet from a
    target word.

    Examples
    ---
    >>> sorted(hamming_circle('abc', 0, 'abc'))
    ['abc']
    >>> sorted(hamming_circle('abc', 1, 'abc'))
    ['aac', 'aba', 'abb', 'acc', 'bbc', 'cbc']
    >>> sorted(hamming_circle('aaa', 2, 'ab'))
    ['abb', 'bab', 'bba']

    """
    for positions in combinations(range(len(word)), n):
        for replacements in product(range(len(alphabet)), repeat=n):
            skip = False
            cousin = list(word)

            for position, replacement in zip(positions, replacements):
                if cousin[position] == alphabet[replacement]:
                    skip = True
                else:
                    cousin[position] = alphabet[replacement]

            if not skip:
                yield ''.join(cousin)