code: def notify_batch_pending(self, batch):
          
          txn_ids = {t.header_signature for t in batch.transactions}
          with self._lock:
              self._pending.add(batch.header_signature)
              self._batch_info[batch.header_signature] = txn_ids
              self._update_observers(batch.header_signature,
                                     ClientBatchStatus.PENDING)
docs: Adds a Batch id to the pending cache, with its transaction ids.
  
          Args:
              batch (str): The id of the pending batch