title: Can't convert expression to float
body: <p>I'm trying to learn the ins and outs of symbolic manipulation in python (I'm a beginner).</p>
  
  <p>I have the following basic code, and the output is giving me an error telling me that it "can't convert expression to float".</p>
  
  <p>What's wrong with this code:</p>
  
  <pre><code>from sympy import *
  from math import *
  
  def h(x):
      return log(0.75392 * x)
  
  x = symbols('x')
  hprime = h(x).diff(x)
  
  print(hprime)
  </code></pre>