title: Count events per range of time in Python
body: <p>The mission is to count how frequent the event (in this case, earthquake) happens per day since 1970 until today (2018-02-05).
  I have this list of time:</p>
  
  <pre><code>['1970-07-31T17:08:05.000Z', '1971-07-14T06:11:30.000Z',
  '1971-07-26T01:23:22.000Z', '1972-12-02T00:19:52.000Z',
  '1976-01-14T16:47:33.500Z', '1977-08-19T06:08:55.000Z',
  '1985-03-03T22:47:07.280Z', '1985-09-19T13:17:47.350Z',
  '1986-05-07T22:47:10.870Z', '1989-05-23T10:54:46.320Z',
  '1994-06-09T00:33:16.230Z', '1994-10-04T13:22:55.840Z',
  '1995-07-30T05:11:23.630Z', '1995-10-09T15:35:53.910Z',
  '1996-02-17T05:59:30.550Z', '1998-03-25T03:12:25.070Z',
  '2000-11-16T04:54:56.740Z', '2001-06-23T20:33:14.130Z',
  '2003-09-25T19:50:06.360Z', '2004-12-23T14:59:04.410Z',
  '2004-12-26T00:58:53.450Z', '2005-03-28T16:09:36.530Z',
  '2006-05-03T15:26:40.290Z', '2006-11-15T11:14:13.570Z',
  '2007-01-13T04:23:21.160Z', '2007-04-01T20:39:58.710Z',
  '2007-08-15T23:40:57.890Z', '2007-09-12T11:10:26.830Z',
  '2009-09-29T17:48:10.990Z', '2010-02-27T06:34:11.530Z',
  '2011-03-11T05:46:24.120Z', '2012-04-11T08:38:36.720Z',
  '2012-04-11T10:43:10.850Z', '2013-02-06T01:12:25.830Z',
  '2013-05-24T05:44:48.980Z', '2014-04-01T23:46:47.260Z',
  '2015-09-16T22:54:32.860Z', '2017-09-08T04:49:19.180Z']
  </code></pre>
  
  <p>From an uncompleted tutorial i have, there's this step</p>
  
  <pre><code>In [114]: for i in range(1,len(time)):
     dt = UTCDateTime(time[i])-UTCDateTime(time[i-1])
     dt = dt / (3600*24)
     inter_event_time.append(dt)
  . . . . . :
  
  In [115]: plt.hist(inter_event_time, bins=range(0,1000,100))
  Out [115]:
  (array([10, 7, 3, 5, 2, 0, 1, 2, 2]),
   array([0, 100, 200, 300, 400, 500, 600, 700, 800, 900]),
   &lt;a list of 9 Patch objects&gt;)
  </code></pre>
  
  <p>and the final outcome is <a href="https://i.stack.imgur.com/MKGvz.png" rel="nofollow noreferrer">this</a> (x axis is days, y axis is how many times it happened). My problem is i don't what inter_event_times supposed to be. Help me pls!</p>