title: Python: return letters not in string
body: <p>I was wondering if there was a method or way to return letters not in a string. </p>
  
  <p>Meaning: Let's say I have the word "testing". <code>"ing" in "testing"</code> returns true but I want to return the letters in <code>"testing"</code> that are <code>NOT in "ing"</code>   --- <code>"test"</code></p>
  
  <p>My plan was to go in this direction: But clearly it's wrong and I've been stuck on this for a while.</p>
  
  <pre><code>str = "testing"
  
  cmpr = "ing"
  
      if cmpr in str
        return *letters* not cmpr in string
  
  output = "test"
  </code></pre>
  
  <p><em>EDIT</em> Better example: (where the letters do not appear in a row)</p>
  
  <p>str = "testing"</p>
  
  <p>cmpr = "tet"</p>
  
  <p>str.replace(cmpr, '', 1) ----> I want it to return "sing" but it still returns "testing"</p>
  
  <p>Can someone please help me solve this?</p>