text: """Spelling Corrector in Python 3; see http://norvig.com/spell-correct.html
  
  Copyright (c) 2007-2016 Peter Norvig
  MIT license: www.opensource.org/licenses/mit-license.php
  """
  
  ################ Spelling Corrector 
  
  import re
  import os
  from collections import Counter
  
  def words(text): return re.findall(r'\w+', text.lower())
  
  WORDS = Counter(words(open(os.path.join(os.path.dirname(__file__),'../../../resources/data/big.txt')).read()))
  
  def P(word, N=sum(WORDS.values())): 
      "Probability of `word`."
      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."
      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))
  '''
  NOTE: Commenting the test suite. Ishwar.
  ################ Test Code 
  
  def unit_tests():
      assert correction('speling') == 'spelling'              # insert
      assert correction('korrectud') == 'corrected'           # replace 2
      assert correction('bycycle') == 'bicycle'               # replace
      assert correction('inconvient') == 'inconvenient'       # insert 2
      assert correction('arrainged') == 'arranged'            # delete
      assert correction('peotry') =='poetry'                  # transpose
      assert correction('peotryy') =='poetry'                 # transpose + delete
      assert correction('word') == 'word'                     # known
      assert correction('quintessential') == 'quintessential' # unknown
      assert words('This is a TEST.') == ['this', 'is', 'a', 'test']
      assert Counter(words('This is a test. 123; A TEST this is.')) == (
             Counter({'123': 1, 'a': 2, 'is': 2, 'test': 2, 'this': 2}))
      
      assert len(WORDS) == 32198
      print (sum(WORDS.values()))
      assert sum(WORDS.values()) == 1115585
      assert WORDS.most_common(10) == [
       ('the', 79808),
       ('of', 40024),
       ('and', 38311),
       ('to', 28765),
       ('in', 22020),
       ('a', 21124),
       ('that', 12512),
       ('he', 12401),
       ('was', 11410),
       ('it', 10681)]
      assert WORDS['the'] == 79808
      assert P('quintessential') == 0
      
      assert 0.07 < P('the') < 0.08
      return 'unit_tests pass'
  
  def spelltest(tests, verbose=False):
      "Run correction(wrong) on all (right, wrong) pairs; report results."
      import time
      start = time.clock()
      good, unknown = 0, 0
      n = len(tests)
      for right, wrong in tests:
          w = correction(wrong)
          good += (w == right)
          if w != right:
              unknown += (right not in WORDS)
              if verbose:
                  print('correction({}) => {} ({}); expected {} ({})'
                        .format(wrong, w, WORDS[w], right, WORDS[right]))
      dt = time.clock() - start
      print('{:.0%} of {} correct ({:.0%} unknown) at {:.0f} words per second '
            .format(good / n, n, unknown / n, n / dt))
      
  def Testset(lines):
      "Parse 'right: wrong1 wrong2' lines into [('right', 'wrong1'), ('right', 'wrong2')] pairs."
      return [(right, wrong)
              for (right, wrongs) in (line.split(':') for line in lines)
              for wrong in wrongs.split()]
  
  if __name__ == '__main__':
      print(unit_tests())
      spelltest(Testset(open('../../../resources/data/spell-testset1.txt')))
      spelltest(Testset(open('../../../resources/data/spell-testset2.txt')))
      #spelltest(Testset(open('spell-testset2.txt')))
  '''