title: Add months to a date in Pandas
body: <p>I'm trying to figure out how to add 3 months to a date in a Pandas dataframe, while keeping it in the date format, so I can use it to lookup a range.</p>
  
  <p>This is what I've tried:</p>
  
  <pre><code>#create dataframe
  df = pd.DataFrame([pd.Timestamp('20161011'),
                     pd.Timestamp('20161101') ], columns=['date'])
  
  #create a future month period
  plus_month_period = 3
  
  #calculate date + future period
  df['future_date'] = plus_month_period.astype("timedelta64[M]")
  </code></pre>
  
  <p>However, I get the following error:</p>
  
  <pre><code>AttributeError: 'int' object has no attribute 'astype'
  </code></pre>