title: Why can't I detect that the tuple is empty?
body: <p>I am using the where function in numpy to look for a one letter string in an array of strings. 
  For example:
  I will look for <code>'U'</code> in <code>['B' 'U' 'A' 'M' 'R' 'O']</code> and get the index of <code>'U'</code>.</p>
  
  <pre><code>letter = 'U'
  row = ['B', 'U', 'A', 'M', 'R', 'O']
  letter_found = np.where(row == letter)
  </code></pre>
  
  <p>However when I am looking for a letter that isn't present in the array of strings I get an empty tuple that looks like this:  </p>
  
  <pre><code>(array([], dtype=int64),)
  </code></pre>
  
  <p>I need to be able to detect when it does not find the letter I am looking for in the array.</p>
  
  <p>I've tried the following:</p>
  
  <pre><code>if not letter_found:
      print 'not found'
  </code></pre>
  
  <p>But this does not work. How can I detect that the <code>tuple</code> returned from the where function in <code>numpy</code> is empty? Is it because one of my variables is possibly the wrong type? I am new at <code>python</code> and programming in general. </p>