code: def previous(self, rows: List[Row]) -> List[Row]:
          
          if not rows:
              return []
          input_row_index = self._get_row_index(rows[0])
          if input_row_index > 0:
              return [self.table_data[input_row_index - 1]]
          return []
docs: Takes an expression that evaluates to a single row, and returns the row that occurs before
          the input row in the original set of rows. If the input row happens to be the top row, we
          will return an empty list.