Get a single cell value stored on this instance.

        For example:

        .. literalinclude:: snippets_table.py
            :start-after: [START bigtable_row_cell_value]
            :end-before: [END bigtable_row_cell_value]

        Args:
            column_family_id (str): The ID of the column family. Must be of the
                form ``[_a-zA-Z0-9][-_.a-zA-Z0-9]*``.
            column (bytes): The column within the column family where the cell
                is located.
            index (Optional[int]): The offset within the series of values. If
                not specified, will return the first cell.

        Returns:
            ~google.cloud.bigtable.row_data.Cell value: The cell value stored
            in the specified column and specified index.

        Raises:
            KeyError: If ``column_family_id`` is not among the cells stored
                in this row.
            KeyError: If ``column`` is not among the cells stored in this row
                for the given ``column_family_id``.
            IndexError: If ``index`` cannot be found within the cells stored
                in this row for the given ``column_family_id``, ``column``
                pair.

def cell_value(self, column_family_id, column, index=0):
        """Get a single cell value stored on this instance.

        For example:

        .. literalinclude:: snippets_table.py
            :start-after: [START bigtable_row_cell_value]
            :end-before: [END bigtable_row_cell_value]

        Args:
            column_family_id (str): The ID of the column family. Must be of the
                form ``[_a-zA-Z0-9][-_.a-zA-Z0-9]*``.
            column (bytes): The column within the column family where the cell
                is located.
            index (Optional[int]): The offset within the series of values. If
                not specified, will return the first cell.

        Returns:
            ~google.cloud.bigtable.row_data.Cell value: The cell value stored
            in the specified column and specified index.

        Raises:
            KeyError: If ``column_family_id`` is not among the cells stored
                in this row.
            KeyError: If ``column`` is not among the cells stored in this row
                for the given ``column_family_id``.
            IndexError: If ``index`` cannot be found within the cells stored
                in this row for the given ``column_family_id``, ``column``
                pair.
        """
        cells = self.find_cells(column_family_id, column)

        try:
            cell = cells[index]
        except (TypeError, IndexError):
            num_cells = len(cells)
            msg = _MISSING_INDEX.format(index, column, column_family_id, num_cells)
            raise IndexError(msg)

        return cell.value