def find_cells(self, column_family_id, column):
        """Get a time series of cells stored on this instance.

        For example:

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

        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 cells
                are located.

        Returns:
            List[~google.cloud.bigtable.row_data.Cell]: The cells stored in the
            specified column.

        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``.
        """
        try:
            column_family = self._cells[column_family_id]
        except KeyError:
            raise KeyError(_MISSING_COLUMN_FAMILY.format(column_family_id))

        try:
            cells = column_family[column]
        except KeyError:
            raise KeyError(_MISSING_COLUMN.format(column, column_family_id))

        return cells