title: Determining Letter Frequency Of Cipher Text
body: <p>I am trying to make a tool that finds the frequencies of letters in some type of cipher text. 
  Lets suppose it is all lowercase a-z no numbers. The encoded message is in a txt file</p>
  
  <p>I am trying to build a script to help in cracking of substitution or possibly transposition ciphers.</p>
  
  <p>Code so far:</p>
  
  <pre><code>cipher = open('cipher.txt','U').read()
  cipherfilter = cipher.lower()
  cipherletters = list(cipherfilter)
  
  alpha = list('abcdefghijklmnopqrstuvwxyz')
  occurrences = {} 
  for letter in alpha:
      occurrences[letter] = cipherfilter.count(letter)
  for letter in occurrences:
      print letter, occurrences[letter]
  </code></pre>
  
  <p>All it does so far is show how many times  a letter appears.
  How would I print the frequency of all letters found in this file.</p>