title: Move index of a string in string.ascii_lowercase
body: <p>I want to change letters in a string by moving the index by 2 steps:
  a --> c, b--> d, c--> e, etc. However, when it gets to the final letters in alphabetical order, I don't know how to make: y --> a and z --> b since it goes out of index when you reach these two letters. Also, I'm sure there's a better way to solve this problem. Thanks!</p>
  
  <pre><code>str = "rpylqjyrc"
  step = 2
  new_str = []
  
  for letter in str:
      if letter in string.ascii_lowercase:
          index = string.ascii_lowercase.index(letter) + step
          word = string.ascii_lowercase[index]
          new_str.append(word)
      else:
          new_str.append(letter)
  
  print("".join(new_str))
  </code></pre>