title: Add missing timestamp in a pandas dataframe
body: <p>I am struggling to add missing timestamp to a dataframe.</p>
  <p>My current output is :</p>
  <pre><code>    start_Local_round           end_Local_round         alarmId
  2020-09-01 00:30:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 00:30:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 02:20:00+00:00   2020-09-01 02:30:00+00:00   155698
  </code></pre>
  <p>And I need something like :</p>
  <pre><code>    start_Local_round           end_Local_round         alarmId
  2020-09-01 00:30:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 00:30:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 00:40:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 00:40:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 00:50:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 00:50:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 01:00:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 01:00:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 01:10:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 01:10:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 01:20:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 01:20:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 01:30:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 01:30:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 01:40:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 01:40:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 01:50:00+00:00   2020-09-01 01:50:00+00:00   15568
  2020-09-01 01:50:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 02:00:00+00:00   2020-09-01 02:50:00+00:00   2560        
  2020-09-01 02:10:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 02:20:00+00:00   2020-09-01 02:30:00+00:00   155698
  2020-09-01 02:20:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 02:30:00+00:00   2020-09-01 02:30:00+00:00   155698
  2020-09-01 02:30:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 02:40:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 02:50:00+00:00   2020-09-01 02:50:00+00:00   2560
  2020-09-01 03:00:00+00:00
  2020-09-01 03:10:00+00:00
  2020-09-01 03:20:00+00:00
  
  </code></pre>
  <p>The aim is to merge it with an another dataframe which have a timestamp with 10 minutes data as well</p>
  <p>I tired to create a dataframe with all the datapoints of the period</p>
  <pre><code>#création des points 10'
  def datetime_range(start, end, delta):
      current = start
      while current &lt; end:
          yield current
          current += delta
  
  min_date = df.start_Local.min().round('10min')
  max_date = df.start_Local.max().round('10min')
          
  dts = [dt.strftime('%Y-%m-%d %H:%M:%S') for dt in datetime_range(min_date, max_date, timedelta(minutes=10))]
  </code></pre>
  <p>But i can't merge it with my original data.</p>
  <p>Do you have any idea to help me ?</p>
  <p>Thanks !!</p>