title: PyCharm Type error Message
body: <p>I'm a newbie trying out ML/DBN in Python (3.4) under PyCharm (Comm.Ed 4.5).
  The following definition</p>
  
  <pre><code>def make_thetas(xmin,xmax,n):
      xs = np.linespace(xmin,xmax,n)
      widths = (xs[1:] - xs[:-1])/2.0
      thetas = xs[:-1] + widths
      return thetas
  </code></pre>
  
  <p>throws the error
  <em>"Class 'tuple' does not define '<strong>sub</strong>', so the '-' operator cannot be used on its instance"</em>
  on the - operator on the third line (widths = ....)
  Any ideas on how to get this code running under PyCharm - it works alright in the interactive Python window.<br>
  Thx.</p>