Simple string permutation

permute.py

def permute(items):
    """
    Return the permutations of the provided set

    :param items: Set of items to permute
    :type items: set
    :return: list of permutations
    :rtype: list
    """

    # If there's only one item (or no items), only one permutation and we already have it
    if len(items) <= 1:
        yield list(items)
        return

    # For every item, we return a list starting with that item, followed by all the permutations of the
    # remaining items.
    result = []
    for item in items:
        # Loop through all the sub-permutations by calling permute with the same set we have now, except with our
        # current item removed
        for sub_permutation in permute(items - {item}):
            # Append the permutation to the result set, prefixed by our current item
            yield [item] + sub_permutation

def permute_string(s):
    """
    Return the permutations of the given string, as a list of strings.

    :param s: String to permute
    :type s: str
    :return: list of permutations
    :rtype: list
    """
    
    # Return a generator that converts the lists into strings for each permutation
    return (''.join(permutation) for permutation in permute(set(s)))

for permutation in permute_string("123"):
    print permutation