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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def set_root(self, index):
 """Set the given index as root index of the combobox :param index: the new root index :type index: QtCore.QModelIndex :returns: None :rtype: None :raises: None """

        if not index.isValid():
            self.setCurrentIndex(-1)
            return
        if self.model() != index.model():
            self.setModel(index.model())
        self.setRootModelIndex(index)
        if self.model().rowCount(index):
            self.setCurrentIndex(0)
        else:
            self.setCurrentIndex(-1)