code: def is_expired(self, time_offset_seconds=0):
          
          now = datetime.datetime.utcnow()
          if time_offset_seconds:
              now = now + datetime.timedelta(seconds=time_offset_seconds)
          ts = boto.utils.parse_ts(self.expiration)
          delta = ts - now
          return delta.total_seconds() <= 0
docs: Checks to see if the Session Token is expired or not.  By default
          it will check to see if the Session Token is expired as of the
          moment the method is called.  However, you can supply an
          optional parameter which is the number of seconds of offset
          into the future for the check.  For example, if you supply
          a value of 5, this method will return a True if the Session
          Token will be expired 5 seconds from this moment.
  
          :type time_offset_seconds: int
          :param time_offset_seconds: The number of seconds into the future
              to test the Session Token for expiration.