How to use the labelme.label_file.LabelFile.is_label_file function in labelme

return

        self.lastOpenDir = dirpath
        self.filename = None
        self.fileListWidget.clear()
        for filename in self.scanAllImages(dirpath):
            if pattern and pattern not in filename:
                continue
            label_file = osp.splitext(filename)[0] + '.json'
            if self.output_dir:
                label_file_without_path = osp.basename(label_file)
                label_file = osp.join(self.output_dir, label_file_without_path)
            item = QtWidgets.QListWidgetItem(filename)
            item.setFlags(Qt.ItemIsEnabled | Qt.ItemIsSelectable)
            if QtCore.QFile.exists(label_file) and \
                    LabelFile.is_label_file(label_file):
                item.setCheckState(Qt.Checked)
            else:
                item.setCheckState(Qt.Unchecked)
            self.fileListWidget.addItem(item)
        self.openNextImg(load=load)

filename = self.settings.value('filename', '')
        filename = str(filename)
        if not QtCore.QFile.exists(filename):
            self.errorMessage(
                self.tr('Error opening file'),
                self.tr('No such file: <b>%s</b>') % filename
            )
            return False
        # assumes same name, but json extension
        self.status(self.tr("Loading %s...") % osp.basename(str(filename)))
        label_file = osp.splitext(filename)[0] + '.json'
        if self.output_dir:
            label_file_without_path = osp.basename(label_file)
            label_file = osp.join(self.output_dir, label_file_without_path)
        if QtCore.QFile.exists(label_file) and \
                LabelFile.is_label_file(label_file):
            try:
                self.labelFile = LabelFile(label_file)
            except LabelFileError as e:
                self.errorMessage(
                    self.tr('Error opening file'),
                    self.tr(
                        "<p><b>%s</b></p>"
                        "<p>Make sure <i>%s</i> is a valid label file."
                    ) % (e, label_file)
                )
                self.status(self.tr("Error reading %s") % label_file)
                return False
            self.imageData = self.labelFile.imageData
            self.imagePath = osp.join(
                osp.dirname(label_file),
                self.labelFile.imagePath,</p>