def insert(self, doc, synced=False):
        doc.id = self.get_next_id()
        doc.synced = synced
        try:
            self.db.docs.insert(doc)
        except Exception as e:
            raise DatabaseException(e)
        return doc
def _acc_grads(g_sum, g_w, g):
  """Accumulate gradients in g, weighted by g_w."""
  return [g_sum_i + g_w * g_i for g_sum_i, g_i in zip(g_sum, g)]