title: Check if a string has unique characters excluding whitespace
body: <p>I'm practicing questions from Cracking the coding interview to become better and just in case, be prepared. The first problem states: Find if a string has all unique characters or not? I wrote this and it works perfectly:</p>
  
  <pre><code>def isunique(string):
      x = []
      for i in string:
          if i in x:
              return False
          else:
              x.append(i)
      return True
  </code></pre>
  
  <p>Now, my question is, what if I have all unique characters like in:
  <strong>'I am J'</strong>
  which would be pretty rare, but lets say it occurs by mere chance, how can I create an exception for the spaces? I a way it doesn't count the space as a character, so the func returns True and not False?</p>