title: A function generating the derivative of f
body: <p>I´m trying to construct a function that return the derivate of <code>f</code>, a function of one variable. </p>
  
  <p>The return value should be a function approximating the derivative of <code>f'</code>
  using the symmetric difference quotient, so that the returned function will compute <code>(f(x+h) -f(x-h))/2h.</code></p>
  
  <p>The function should start like this:</p>
  
  <p><code>def derivative(f, x):</code></p>
  
  <p>which should approximate the derivative of function f around the point x. 
  Does anyone have a clue what type of code I can use to construct this type of function?</p>
  
  <p>/Alex</p>