title: TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'
body: <p>When I try to use  function inside another function</p>
  
  <p><strong>Error</strong></p>
  
  <blockquote>
    <p>TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'</p>
  </blockquote>
  
  <pre><code># Function to calculate 2D circularity ratio      
  def defineCircularRatio(perim2D, area2D): 
  
      circularity_ratio = (4*math.pi*area2D)/(perim2D**2)
  
      return circularity_ratio
  
      print "The 2D circul_ratio is:", circularity_ratio
  </code></pre>
  
  <p>perimeter and area  -calculated by other functions.</p>