title: count the total numbers of unique letters occurred once in a string in python?
body: <pre><code>a = 'abhishek'
  count = 0
  
  for x in a:
      if x in a:
          count += 1 
  print(count) 
  </code></pre>
  
  <p>I have tried this but it gives me the total number of letters. I want only a unique latter that occurs only once.</p>