title: ValueError: The truth value of a Series is ambiguous - check a value in pandas column
body: <p>I am trying to check of my panda column has a specific value using the code below:</p>
  
  <pre><code>if not df['my_col'].str.contains('my_value'):
  </code></pre>
  
  <p>But I got the following errors:</p>
  
  <pre><code>  File "/Users/edamame/workspace/git/process/data_stats.py", line 225, in &lt;module&gt;
      if not df['my_col'].str.contains('my_value'):
    File "/Users/edamame/workspace/git/process/venv/lib/python3.4/site-packages/pandas/core/generic.py", line 917, in __nonzero__
      .format(self.__class__.__name__))
  ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().
  </code></pre>
  
  <p>Any idea what I did wrong and how to fix it? Thanks!</p>