title: boolean subtract DeprecationWarning
body: <p>I recently upgraded to numpy 1.9dev.
  (For improved OpenBlas support).</p>
  
  <p>I have some code that does <code>x-y</code> 
  Where <code>x</code> and <code>y</code> are samples from a probability distribution.
  If the distribution is Bernoulli, then they are boolean.
  If the distribution is Gaussian, then they are floats.</p>
  
  <p>where depending on the path followed <code>x</code> and <code>y</code>
  might be bools or floats.
  I don't have to care as python has duck-typing.
  If it can subtract then it is a valid value for <code>x</code> and <code>y</code></p>
  
  <p>I get this warning:</p>
  
  <blockquote>
    <p>DeprecationWarning: numpy boolean subtract (the binary <code>-</code> operator)
    is deprecated, use the bitwise_xor (the <code>^</code> operator) or the
    logical_xor function instead.</p>
  </blockquote>
  
  <p>I have made the warning go away, by casting it to always be a float.
  This may be a good thing since it makes the code more consistent at a lower level.
  (Not sold on that as a good thing).</p>
  
  <p>What is the correct action to be taking?
  I can't use boolean or bitwise xor as when <code>x</code> and <code>y</code> are floats this will break.
  It would be ugly to make the code branch on the type of <code>x</code> and <code>y</code>.</p>