code: def put(self, entity):
      
      self._cur_batch.put(entity)
      self._num_mutations += 1
      if self._num_mutations >= MAX_MUTATIONS_IN_BATCH:
        self.commit()
        self.begin()
docs: Adds mutation of the entity to the mutation buffer.
  
      If mutation buffer reaches its capacity then this method commit all pending
      mutations from the buffer and emties it.
  
      Args:
        entity: entity which should be put into the datastore