def _do_open_file (self, fpath):
     """
         effective procedure for opening file to import;
     """
     # is a genuine CSV file?
     if self.is_csv(fpath):
         # update options dir
         self.options["dirs"]["namedb_import_dir"] = OP.dirname(fpath)
         # update current path
         self.current_path = fpath
         # update file infos
         self.container.get_stringvar("lbl_file_path")\
             .set(P.shorten_path(fpath, limit=50))
         # show contents preview
         self._fill_preview(fpath)
         # update field assignment order
         self._fill_fields(fpath)
         # prepare to import
         self.BTN_IMPORT.configure(
             text=_("Import"), command=self.slot_file_import
         )
         self.stop_import = False
     # not a CSV file
     else:
         # notify user
         MB.showwarning(
             title=_("Attention"),
             message=_("Invalid CSV file format. Not supported."),
             parent=self,
         )