Есть QListWidgetItem.setData :
item = QListWidgetItem('Text', parent)
data = ('foo', 'bar', [1, 2, 3])
item.setData(Qt.UserRole, data)
...
# QVariant version 1 API (python2 default)
print item.data(Qt.UserRole).toPyObject()
# QVariant version 2 API (python3 default)
print item.data(Qt.UserRole)