rot13.txt

Backwards when rot13'd:
an <-> na
fans <-> snaf
fobs <-> sbof
gnat <-> tang
ravine <-> enivar
re <-> er
robe <-> ebor
serf <-> fres
tang <-> gnat
thug <-> guht
uh <-> hu

Other word when rot13'd:
ah <-> nu
aha <-> nun
ant <-> nag
balk <-> onyx
bar <-> one
barf <-> ones
be <-> or
bin <-> ova
crag <-> pent
ebbs <-> roof
envy <-> rail
errs <-> reef
flap <-> sync
fur <-> she
gel <-> try
gnat <-> tang
if <-> vs
irk <-> vex

script.py

from string import ascii_lowercase as alphabet


def get_words(words=[]):
    if not words:
        with open('/usr/share/dict/words') as word_file:
            for word in word_file:
                word = word.strip()
                if len(word) > 1 and all(c in alphabet for c in word):
                    words.append(word)

    return words

def rot13_table():
    return str.maketrans(alphabet, alphabet[13:] + alphabet[:13])

def rot13(word, table=rot13_table()):
    return word.translate(table)

def backwards_rot13s():
    back_words = []

    for word in get_words():
        backwards = word[::-1]
        if backwards == rot13(word):
            back_words.append((word, backwards))

    return back_words

def other_word_rot13s():
    words = get_words()
    set_words = set(words)
    other_words = []

    for word in words:
        if word.startswith('n'):
            break

        other_word = rot13(word)
        if other_word in set_words:
            other_words.append((word, other_word))

    return other_words

def main():
    print("Backwards when rot13'd:")
    for (word, backwards) in backwards_rot13s():
        print('{} <-> {}'.format(word, backwards))

    print()

    print("Other word when rot13'd:")
    for (word, other) in other_word_rot13s():
        print('{} <-> {}'.format(word, other))

if __name__ == '__main__':
    main()