title: Return count for specific value in pandas .value_counts()?
body: <p>Assume running pandas' dataframe['prod_code'].value_counts() and storing result as 'df'.  The operation outputs:</p>
  
  <pre><code>125011  90300
     762  72816
    None  55512
    7156  14892 
   75162   8825
  </code></pre>
  
  <p>How would I extract the count for None?  I'd expect the result to be 55512.</p>
  
  <p>I've tried </p>
  
  <pre><code>&gt;&gt;&gt; df.loc[df.index.isin(['None'])]
  &gt;&gt;&gt; Series([], Name: prod_code, dtype: int64)
  </code></pre>
  
  <p>and also </p>
  
  <pre><code>&gt;&gt;&gt; df.loc['None']
  &gt;&gt;&gt; KeyError: 'the label [None] is not in the [index]'
  </code></pre>