title: How to add a new columns which is a circular seriers number in pandas?
body: <p>For example:</p>
  
  <pre><code> A      B
  1981    1
  1981    2
  1981    3
  1981    4   
  1982    1
  1982    2
  1982    3
  1982    4
  1983    1
  1983    2
  1983    3
  1983    4
  1984    1
  1984    2
  1984    3
  1984    4
  1985    1
  </code></pre>
  
  <p>column A is existed , B is I want to add. How to generate B?</p>