spelling.py

# Sourced from
# http://norvig.com/spell-correct.html
# Use set_dictionary to set the dictionary of words

import os
import re
from collections import Counter

WORDS = None
N = None

def set_dictionary(word_list):
    global WORDS
    global N
    WORDS = Counter(word_list)
    N=sum(WORDS.values())


def words(text):
    return re.findall(r'\w+', text.lower())

    
def P(word):
    "Probability of `word`."
    if not N:
        return 0
    
    return WORDS[word] / N

def correction(word):
    "Most probable spelling correction for word."
    return max(candidates(word), key=P)

def candidates(word): 
    "Generate possible spelling corrections for word."
    return (known([word]) or known(edits1(word)) or known(edits2(word)) or [word])

def known(words):
    "The subset of `words` that appear in the dictionary of WORDS."
    if not WORDS:
        return None
    
    return set(w for w in words if w in WORDS)

def edits1(word):
    "All edits that are one edit away from `word`."
    letters    = 'abcdefghijklmnopqrstuvwxyz'
    splits     = [(word[:i], word[i:])    for i in range(len(word) + 1)]
    deletes    = [L + R[1:]               for L, R in splits if R]
    transposes = [L + R[1] + R[0] + R[2:] for L, R in splits if len(R)>1]
    replaces   = [L + c + R[1:]           for L, R in splits if R for c in letters]
    inserts    = [L + c + R               for L, R in splits for c in letters]
    return set(deletes + transposes + replaces + inserts)

def edits2(word): 
    "All edits that are two edits away from `word`."
    return (e2 for e1 in edits1(word) for e2 in edits1(e1))