code: def _convert_strls(self, data):
          
          convert_cols = [
              col for i, col in enumerate(data)
              if self.typlist[i] == 32768 or col in self._convert_strl]
  
          if convert_cols:
              ssw = StataStrLWriter(data, convert_cols)
              tab, new_data = ssw.generate_table()
              data = new_data
              self._strl_blob = ssw.generate_blob(tab)
          return data
docs: Convert columns to StrLs if either very large or in the
          convert_strl variable