Proceed to a given step

def _set_step(self, step):
        """Proceed to a given step"""
        new_tab = self.tab_widget.currentIndex() + step
        assert new_tab < self.tab_widget.count() and new_tab >= 0
        if new_tab == self.tab_widget.count()-1:
            try:
                self.table_widget.open_data(self._get_plain_text(),
                                        self.text_widget.get_col_sep(),
                                        self.text_widget.get_row_sep(),
                                        self.text_widget.trnsp_box.isChecked(),
                                        self.text_widget.get_skiprows(),
                                        self.text_widget.get_comments())
                self.done_btn.setEnabled(True)
                self.done_btn.setDefault(True)
                self.fwd_btn.setEnabled(False)
                self.back_btn.setEnabled(True)
            except (SyntaxError, AssertionError) as error:
                QMessageBox.critical(self, _("Import wizard"),
                            _("<b>Unable to proceed to next step</b>"
                              "<br><br>Please check your entries."
                              "<br><br>Error message:<br>%s") % str(error))
                return
        elif new_tab == 0:
            self.done_btn.setEnabled(False)
            self.fwd_btn.setEnabled(True)
            self.back_btn.setEnabled(False)
        self._focus_tab(new_tab)