code: def _chk_fields(field_data, field_formatter):
          
          if len(field_data) == len(field_formatter):
              return
          len_dat = len(field_data)
          len_fmt = len(field_formatter)
          msg = [
              "FIELD DATA({d}) != FORMATTER({f})".format(d=len_dat, f=len_fmt),
              "DAT({N}): {D}".format(N=len_dat, D=field_data),
              "FMT({N}): {F}".format(N=len_fmt, F=field_formatter)]
          raise Exception("\n".join(msg))
docs: Check that expected fields are present.