title: Python tzinfo and daylight time
body: <p>(I am new to Python and Google App Engine, please forgive me if my questions seem basic).</p>
  
  <p>I'm having a helluva time trying to manage multiple user timezones in my Google App Engine application.</p>
  
  <p>Here are my constraints:</p>
  
  <ol>
  <li>If a user enters the time on an input, it will be local time (including DST, when appropriate).</li>
  <li>If a user does not enter the time, the system must enter it for them in their local time (including DST, when appropriate).</li>
  <li>When the date and time are displayed to the user, it must be in their local time (including DST, when appropriate)</li>
  </ol>
  
  <p>I understand that time will be internally stored as UTC with a tzinfo object and that the App Engine will store the Models with UTC time.</p>
  
  <p>I previously thought I had this all worked out by asking the user to specify their time zone in their preferences.  Then, I would simply load their preferences and add that tzinfo to any datetime objects in reference to that user.</p>
  
  <p>However, our recent daylight saving time broke it.  It turns out that I had not correctly implemented the dst() in my tzinfo objects.  As I understand it, I must determine if DST is currently on, and if so, return the correct offset for the tzinfo.</p>
  
  <p>The problem is, I have no idea how to determine if the timezone's daylight time is current or not.  Am I missing something obvious?</p>