title: Create 6 monthly periods in Python
body: <p>I have a dataset (lets just call it <code>df</code>) containing a populated <code>ID column</code> and a date column called <code>Start_of_Intervention</code>. </p>
  
  <p>I'm trying to calculate <code>6 month periods</code> for a period of 5 years before and after this <code>Start_of_Intervention</code> date. </p>
  
  <p><code>The dates are formatted as 20/02/2015 etc.</code></p>
  
  <p>I think I need to use <code>datetime.date</code> as I'm not interested in the time part, but am having trouble linking my dataset to any of the date functions. </p>
  
  <p>This code does not seem to work well:</p>
  
  <pre><code>dt['START_OF_INTERVENTION2']=dt['START_OF_INTERVENTION'].astype(str) 
  
  dt['START_OF_INTERVENTION3'] = dt['START_OF_INTERVENTION2'].apply( 
  lambda x: 
  x+relativedelta(months=+6)
  </code></pre>
  
  <p>Can anyone advise please?</p>