title: python convert 10 digits datetimestamp to 13 digit GMT timestamp
body: <p>I receive a timestamp from a server like this 1512543958 &amp; when i send back requests in headers i see a 13 digit GMT time stamp like this 1512544485819</p>
  
  <p>By changing the time to local using the code below i get <em>2017-12-06 12:35:58</em></p>
  
  <pre><code>print(datetime.datetime.fromtimestamp(int("1512544474")).strftime('%Y-%m-%d %H:%M:%S')
  </code></pre>
  
  <p>&amp; when i apply the code below i get <em>'Wed 06 Dec 2017 07:14:45 GMT'</em></p>
  
  <pre><code>time.strftime("%a %d %b %Y %H:%M:%S GMT", time.gmtime(1512544485819 / 1000.0))
  </code></pre>
  
  <p>So basically i need a python function that takes the 10 digit date timestamp as argument &amp; returns 13 digit GMT date timestamp </p>
  
  <p>example input 1512544474<br>
  expected output 1512544485819 </p>