code: def _check_years(self, cell, prior_year):
          '''
          Helper method which defines the rules for checking for existence of a year indicator. If the
          cell is blank then prior_year is used to determine validity.
          '''
          # Anything outside these values shouldn't auto
          # categorize to strings
          min_year = 1900
          max_year = 2100
  
          # Empty cells could represent the prior cell's title,
          # but an empty cell before we find a year is not a title
          if is_empty_cell(cell):
              return bool(prior_year)
          # Check if we have a numbered cell between min and max years
          return is_num_cell(cell) and cell > min_year and cell < max_yeaf _check_years(self, cell, prior_year):
          '''
          Helper method which defines the rules for checking for existence of a year indicator. If the
          cell is blank then prior_year is used to determine validity.
          '''
          # Anything outside these values shouldn't auto
          # categorize to strings
          min_year = 1900
          max_year = 2100
  
          # Empty cells could represent the prior cell's title,
          # but an empty cell before we find a year is not a title
          if is_empty_cell(cell):
              return bool(prior_year)
          # Check if we have a numbered cell between min and max years
          return is_num_cell(cell) and cell > min_year and cell < max_year
docs: Helper method which defines the rules for checking for existence of a year indicator. If the
          cell is blank then prior_year is used to determine validity.