How to Write a Spelling Corrector (incidentally, how cool is python!)

// January 8th, 2010 // Tech

import re, collections

def words(text): return re.findall('[a-z]+', text.lower())

def train(features):

model = collections.defaultdict(lambda: 1)

for f in features:

model[f] += 1

return model

NWORDS = train(words(file('big.txt').read()))

alphabet = 'abcdefghijklmnopqrstuvwxyz'

def edits1(word):

splits = [(word[:i], word[i:]) for i in range(len(word) + 1)]

deletes = [a + b[1:] for a, b in splits if b]

transposes = [a + b[1] + b[0] + b[2:] for a, b in splits if len(b)>1]

replaces = [a + c + b[1:] for a, b in splits for c in alphabet if b]

inserts = [a + c + b for a, b in splits for c in alphabet]

return set(deletes + transposes + replaces + inserts)

def known_edits2(word):

return set(e2 for e1 in edits1(word) for e2 in edits1(e1) if e2 in NWORDS)

def known(words): return set(w for w in words if w in NWORDS)

def correct(word):

candidates = known([word]) or known(edits1(word)) or known_edits2(word) or [word]

return max(candidates, key=NWORDS.get)