title: differentiating a polynomial interpolated set of data points
body: <p>I'm aware that we can us <code>numpy</code> to differentiate polynomials with the following:</p>
  
  <pre><code>f = numpy.poly1d([1, 0, 1])
  f.deriv()
  </code></pre>
  
  <p>I've tried interpolating a set of data points and performing <code>deriv()</code> on the resulting polynomial.</p>
  
  <pre><code>from scipy import interpolate
  
  x = [-2,-1,2]
  y = [-2,1,-1] 
  
  f = interpolate.interp1d(x, y)
  f.deriv()
  </code></pre>
  
  <p>But the object <code>f</code> is of different type.</p>
  
  <p>Basically, how might I convert <code>f</code> to a <code>numpy</code> polynomial object ready for differentiation?</p>
  
  <p>Thanks a lot!</p>