title: Change each character in string to the next character in alphabet
body: <p>I am coding in Python 2.7 using PyCharm on Ubuntu.</p>
  
  <p>I am trying to create a function that will take a string and change each character to the character that would be next in the alphabet.</p>
  
  <pre><code>def LetterChanges(str):
      # code goes here
      import string
      ab_st = list(string.lowercase)
      str = list(str)
      new_word = []
      for letter in range(len(str)):
          if letter == "z":
              new_word.append("a")
          else:
              new_word.append(ab_st[str.index(letter) + 1])
          new_word = "".join(new_word)
      return new_word
  
  
  # keep this function call here
  print LetterChanges(raw_input())
  </code></pre>
  
  <p>When I run the code I get the following error:</p>
  
  <pre><code>/usr/bin/python2.7 /home/vito/PycharmProjects/untitled1/test.py
  test
  Traceback (most recent call last):
    File "/home/vito/PycharmProjects/untitled1/test.py", line 17, in &lt;module&gt;
      print LetterChanges(raw_input())
    File "/home/vito/PycharmProjects/untitled1/test.py", line 11, in LetterChanges
      new_word.append(ab_st[str.index(letter) + 1])
  ValueError: 0 is not in list
  
  Process finished with exit code 1
  </code></pre>
  
  <p>What am I doing wroing in line 11? How can I get the following character in the alphabet for each character and append it to the new list?</p>
  
  <p>Many thanks.</p>