docs: def read_existing_paths(bt_table):
      """Return the SGF filename for each existing eval record."""
      rows = bt_table.read_rows(
          filter_=row_filters.ColumnRangeFilter(
              METADATA, SGF_FILENAME, SGF_FILENAME))
      names = (row.cell_value(METADATA, SGF_FILENAME).decode() for row in rows)
      processed = [os.path.splitext(os.path.basename(r))[0] for r in names]
      return processed