How to Write a Spelling Corrector

How to Write a Spelling Corrector.

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)

The code defines the function correct, which takes a word as input and returns a likely correction of that word. For example:

>>> correct('speling')
'spelling'
>>> correct('korrecter')
'corrector'
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