title: Type of element in Pandas DataFrame does not agree with filter
body: <p>I wanna check types of elements in Pandas DataFrame columns, but doing it the Pandas way, vectorized, not using loops.
  As a toy example:</p>
  <p><code>dic = pd.DataFrame({'a': [1,2,3], 'b':list('abc')})</code></p>
  <p>So, when I do:</p>
  <p><code>dic[dic['a'] == int]</code></p>
  <p>I expect to see the whole DataFrame, since all of the elements of the column 'a' are int. However, the output shows only the header of the DataFrame. In reverse, when I do:</p>
  <p><code>dic[dic['a'] != int]</code></p>
  <p>It outputs the whole DataFrame.
  I don't understand why.</p>