code: def update(self, validate=False):
          
          rs = self.connection.get_all_snapshots([self.id])
          if len(rs) > 0:
              self._update(rs[0])
          elif validate:
              raise ValueError('%s is not a valid Snapshot ID' % self.id)
          return self.progress
docs: Update the data associated with this snapshot by querying EC2.
  
          :type validate: bool
          :param validate: By default, if EC2 returns no data about the
                           snapshot the update method returns quietly.  If
                           the validate param is True, however, it will
                           raise a ValueError exception if no data is
                           returned from EC2.