title: python date unix 1 day is lost
body: <p>I have an error in python, when extracting one day. I'm converting to unix and extracting one day, yet the 11th of march - is always missing, no matter how big the dataset. Could anyone tell me what might be the error ?</p>
  
  <pre><code>from time import localtime, mktime, strptime, strftime
  day = str(20180313)
  one_day = 86400
  for i in range(1,5):
      print(day)
      previous_day_unix = int( mktime( strptime( day, "%Y%m%d")))-one_day
      day = strftime("%Y%m%d", localtime(int(previous_day_unix)))
      print(day)
  </code></pre>