title: how to print words excluding particular letter string?
body: <p>I need to write a program to prompt the user to enter a string of forbidden letters and then print the number of words that don’t contain any of them</p>
  
  <p>This is what I have:</p>
  
  <pre><code>fin=open("demo.txt",'r')
  letters=str(raw_input("Enter the key you want to exclude"))
  def avoid ():   
      for line in fin:
          word = line.strip()
          for l in letters:
              if l not in word: 
                  print word          
  avoid()
  </code></pre>
  
  <p>If I use the <strong>in</strong> keyword it prints all the words that have the particular strings. But it's not working the same when I am using <strong>not in</strong>.</p>