code: def insert(self, database, key, value, callback=None):
          
          token = self._get_token()
          self._enqueue(self._PendingItem(token, BlobCommand(token=token, database=database,
                                                             content=InsertCommand(key=key.bytes, value=value)),
                                          callback))
docs: Insert an item into the given database.
  
          :param database: The database into which to insert the value.
          :type database: .BlobDatabaseID
          :param key: The key to insert.
          :type key: uuid.UUID
          :param value: The value to insert.
          :type value: bytes
          :param callback: A callback to be called on success or failure.