title: Get indices that satisfy some criteria
body: <p>In Pandas, how can I get a list of indices of a series/dataframe for the entries that satisfy some property?</p>
  
  <p>The following returns a <code>Series</code> object</p>
  
  <pre><code>my_dataframe.loc[:,'some_column'] == 'some_value'
  </code></pre>
  
  <p>that looks like this:</p>
  
  <pre><code>519     True
  509    False
  826    False
  503    False
  511    False
  512    False
  500    False
  507    False
  516     True
  504    False
  521    False
  510    False
  351    False
  522    False
  526    False
  517    False
  501    False
  </code></pre>
  
  <p>but what I want is two lists, one with</p>
  
  <pre><code>[519, 516]
  </code></pre>
  
  <p>and one with the rest of indices. How can I do this in Pandas?</p>