# Frequency Finder

# frequency taken from http://en.wikipedia.org/wiki/Letter_frequency
englishLetterFreq = {'E': 12.70, 'T': 9.06, 'A': 8.17, 'O': 7.51, 'I': 6.97,
 'N': 6.75, 'S': 6.33, 'H': 6.09, 'R': 5.99, 'D': 4.25,
 'L': 4.03, 'C': 2.78, 'U': 2.76, 'M': 2.41, 'W': 2.36,
 'F': 2.23, 'G': 2.02, 'Y': 1.97, 'P': 1.93, 'B': 1.29,
 'V': 0.98, 'K': 0.77, 'J': 0.15, 'X': 0.15, 'Q': 0.10,
 'Z': 0.07}
ETAOIN = 'ETAOINSHRDLCUMWFGYPBVKJXQZ'
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

def getLetterCount(message):
 letterCount = {'A': 0, 'B': 0, 'C': 0, 'D': 0, 'E': 0, 'F': 0, 'G': 0, 'H': 0,
 'I': 0, 'J': 0, 'K': 0, 'L': 0, 'M': 0, 'N': 0, 'O': 0, 'P': 0,
 'Q': 0, 'R': 0, 'S': 0, 'T': 0, 'U': 0, 'V': 0, 'W': 0, 'X': 0,
 'Y': 0, 'Z': 0}
 for letter in message.upper():
 if letter in LETTERS:
 letterCount[letter] += 1

 return letterCount

def getItemAtIndexZero(x):
 return x[0]

def getFrequencyOrder(message):
 letterToFreq = getLetterCount(message)
 freqToLetter = {}
 for letter in LETTERS:
 if letterToFreq[letter] not in freqToLetter:
 freqToLetter[letterToFreq[letter]] = [letter]
 else:
 freqToLetter[letterToFreq[letter]].append(letter)

 for freq in freqToLetter:
 freqToLetter[freq].sort(key = ETAOIN.find, reverse = True)
 freqToLetter[freq] = ''.join(freqToLetter[freq])

 freqPairs = list(freqToLetter.items())
 freqPairs.sort(key = getItemAtIndexZero, reverse = True)

 freqOrder = []
 for freqPair in freqPairs:
 freqOrder.append(freqPair[1])

 return ''.join(freqOrder)

def englishFreqMatchScore(message):
 '''
 >>> englishFreqMatchScore('Hello World')
 1
 '''
 freqOrder = getFrequencyOrder(message)
 matchScore = 0
 for commonLetter in ETAOIN[:6]:
 if commonLetter in freqOrder[:6]:
 matchScore += 1

 for uncommonLetter in ETAOIN[-6:]:
 if uncommonLetter in freqOrder[-6:]:
 matchScore += 1

 return matchScore

if __name__ == '__main__':
 import doctest
 doctest.testmod()