title: Find common characters between two strings
body: <p>I am trying to print the common letters from two different user inputs <strong>using a <code>for</code> loop</strong>. (I need to do it using a for loop.) I am running into two problems: 1. My statement "If char not in output..." is not pulling unique values. 2. The output is giving me a list of individual letters rather than a single string.  I tried the split the output but split ran into a type error. </p>
  
  <pre><code>wrd = 'one'
  sec_wrd = 'toe'
  
  def unique_letters(x): 
      output =[]
      for char in x: 
          if char not in output and char != " ": 
              output.append(char)
      return output
  
  final_output = (unique_letters(wrd) + unique_letters(sec_wrd))
  
  print(sorted(final_output))
  </code></pre>