title: Add new rows to pandas dataframe with reference with other Row?
body: <p>df:</p>
  <pre><code>End_Dt_Id Start_Date     End_Date
  18AUG19   12-08-2019    18-08-2019  -- date format DD/MM/YYYY
  25AUG19   19-08-2019    25-08-2019
  01SEP19   26-08-2019    01-09-2019
  08SEP19   02-09-2019    08-09-2019
  15SEP19   09-09-2019    15-09-2019
  22SEP19   16-09-2019    22-09-2019
  12SEP19   23-09-2019    29-09-2019
  </code></pre>
  <p>I need to add 4 more weeks to my dataframe which will depend upon last week in my df,
  for example the last week would be this row &quot;29SEP19   23-09-2019   29-09-2019&quot; because of max(End_Date), there after i need to add four more weeks as shown in the output.</p>
  <p>df_output:</p>
  <pre><code>End_Dt_Id Start_Date     End_Date
  18AUG19   12-08-2019    18-08-2019  -- date format DD/MM/YYYY
  25AUG19   19-08-2019    25-08-2019
  01SEP19   26-08-2019    01-09-2019
  08SEP19   02-09-2019    08-09-2019
  15SEP19   09-09-2019    15-09-2019
  22SEP19   16-09-2019    22-09-2019
  29SEP19   23-09-2019    29-09-2019
  05OCT19   30-09-2019    05-10-2019
  12OCT19   06-10-2019    12-10-2019
  19OCT19   13-10-2019    19-10-2019
  26OCT19   20-10-2019    26-10-2019
  </code></pre>