title: How to add new rows to existing data-frame if there is no data in dataframe python pandas
body: <p>Need to add new rows to existing data-frame if there is no data in dataframe.In my dataframe,If mcahine on it gives data with time and status(On/off) <strong>for every 30 seconds</strong>. But machine off,there is no data in dataframe.
  df:</p>
  <pre><code> Time                      Engine On/Off
  2021-03-08 00:00:24+05:30   1
  2021-03-08 00:00:54+05:30   1
  2021-03-08 00:01:24+05:30   1
  2021-03-08 00:01:54+05:30   1
  </code></pre>
  <p>ex: first row 00:00:24 and then after 30 secods,secods data point  00:00:54.</p>
  <p>Here i need to append rows if next time point data not available(current state + 30 seconds). With time and Engine On/Off state as 0.</p>