title: Quick way to check if the pandas series contains a negative value
body: <p>What is the quickest way to check if the given pandas series contains a negative value.</p>
  
  <p>For example, for the series <code>s</code> below the answer is <code>True</code>.</p>
  
  <pre><code>s = pd.Series([1,5,3,-1,7])
  
  0    1
  1    5
  2    3
  3   -1
  4    7
  dtype: int64
  </code></pre>