"""This module contains code from
Think Python by Allen B. Downey
http://thinkpython.com

Copyright 2012 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html

"""

from anagram_sets import *

def metathesis_pairs(d):
    """Print all pairs of words that differ by swapping two letters.

    d: map from word to list of anagrams
    """
    for anagrams in d.itervalues():
        for word1 in anagrams:
            for word2 in anagrams:
                if word1 < word2 and word_distance(word1, word2) == 2:
                    print word1, word2


def word_distance(word1, word2):
    """Computes the number of differences between two words.

    word1, word2: strings

    Returns: integer
    """
    assert len(word1) == len(word2)

    count = 0
    for c1, c2 in zip(word1, word2):
        if c1 != c2:
            count += 1

    return count


if __name__ == '__main__':
    d = all_anagrams('words.txt')
    metathesis_pairs(d)