title: Querying for NaN and other names in Pandas
body: <p>Say I have a dataframe <code>df</code> with a column <code>value</code> holding some float values and some <code>NaN</code>. How can I get the part of the dataframe where we have <code>NaN</code> <strong>using the query syntax</strong>?</p>
  
  <p>The following, for example, does not work:</p>
  
  <pre><code>df.query( '(value &lt; 10) or (value == NaN)' )
  </code></pre>
  
  <p>I get <code>name NaN is not defined</code> (same for <code>df.query('value ==NaN')</code>)</p>
  
  <p>Generally speaking, is there any way to use numpy names in query, such as <code>inf</code>, <code>nan</code>, <code>pi</code>, <code>e</code>, etc.?</p>