title: Check if only one variable in a list of variables is set
body: <p>I'm looking for a simple method to check if only one variable in a list of variables has a True value.
  I've looked at this <a href="https://stackoverflow.com/questions/432842/how-do-you-get-the-logical-xor-of-two-variables-in-python">logical xor post</a> and is trying to find a way to adapt to multiple variables and only one true.</p>
  
  <p>Example</p>
  
  <pre><code>&gt;&gt;&gt;TrueXor(1,0,0)
  True
  
  &gt;&gt;&gt;TrueXor(0,0,1)
  True
  
  &gt;&gt;&gt;TrueXor(1,1,0)
  False
  
  &gt;&gt;&gt;TrueXor(0,0,0,0,0)
  False
  </code></pre>