title: Get tz offset from string
body: <p>I have a date which is in local time:</p>
  
  <pre><code>date: "2013-12-02 22:00:00"
  </code></pre>
  
  <p>and another value the tz:</p>
  
  <pre><code>timezone_offset: "GMT-0800"
  </code></pre>
  
  <p>If I : <code>dateutil.parser.parse(date).isoformat()</code> I will get:</p>
  
  <pre><code>"2013-12-02T22:00:00+0000"
  </code></pre>
  
  <hr>
  
  <p>I want to implement the <code>date</code> in ISO format with the tz info and get a result of:</p>
  
  <pre><code>"2013-12-02T22:00:00-0800"
  </code></pre>
  
  <p>Something close to: <code>parse(date,tzinfos=??).isoformat()</code> ? How can I get the tzinfo from the string <code>timezone_offset</code> ?</p>