title: UserWarning: converting a masked element to nan
body: <p>Executing a python script (way to long to include here) I wrote leads to a warning message. I don't know at which line in my code this gets raised. How can I get this information?</p>
  
  <p>Furthermore, what does this mean exactly? In fact, I didn't know I was using a masked array of some sort?</p>
  
  <pre><code>/usr/lib/pymodules/python2.7/numpy/ma/core.py:3785: UserWarning: Warning: converting a masked element to nan.
  warnings.warn("Warning: converting a masked element to nan.")
  </code></pre>