title: python-3.5, timestamp to YYYYmmDDHHMMSS
body: <p>Hello to every saturday workers!
  I need to convert a timestamp to YYYYmmDDHHMMSS. The following works well</p>
  
  <pre><code>    timestamp=now_var[27:38]                      # timestamp string 
  dth_now=(                               # string date heure 
      datetime.datetime.fromtimestamp(
          int(timestamp)
       ).strftime('%Y%m%d_%H%M%S')
  )                                       # a string
  </code></pre>
  
  <p>but gives an alert</p>
  
  <pre><code>  File "C:\_Python\kWh_compare.py", line 35, in &lt;module&gt;
  ).strftime('%Y%m%d_%H%M%S')
  ValueError: invalid literal for int() with base 10: ''
  </code></pre>
  
  <p>Where is the problem ?
  thanks</p>