How to filter a pandas dataframe based on the length of a entry
<p>In a pandas dataframe I have a field 'amp' that should be populated by a list of length 495.  Is there a panda-ic way to quickly filter on this length, such that all rows with field 'amp' are not equal to 495 are dropped?</p>
<p>I tried</p>
<pre><code>df[len(df['amp']) == 495]
</code></pre>
<p>and this returned</p>
<pre><code>KeyError: False
</code></pre>