title: How to convert Period string to actual Period type
body: <p>I have a column of data such as <code>'1971q1'</code>, <code>'1972q2'</code>, etc. (year followed by quarter) When I do:</p>
  
  <pre><code>print(type(df.Quarterly))
  </code></pre>
  
  <p>the answer is <code>Series</code></p>
  
  <p>What I need is to "cast"/convert this column to a genuine pd.Period type so I can do simple time algebra with it.  Thank you</p>