def show_info(self):
        """
        displays the doc string of the selected element
        """

        sender = self.sender()
        tree = sender.parent()
        index = tree.selectedIndexes()
        info = ''
        if index != []:
            index = index[0]
            name = str(index.model().itemFromIndex(index).text())

            if name in set(list(self.elements_from_file.keys()) + list(self.elements_selected.keys())):
                probe_name = None
                instrument_name = name
            else:
                instrument_name = str(index.model().itemFromIndex(index).parent().text())
                probe_name = name



            module = __import__('pylabcontrol.instruments', fromlist=[instrument_name])
            if probe_name is None:
                info = getattr(module, instrument_name).__doc__
            else:
                if probe_name in list(getattr(module, instrument_name)._PROBES.keys()):
                    info = getattr(module, instrument_name)._PROBES[probe_name]

        if info is not None:
            self.lbl_info.setText(info)