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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 get_variables(self):
 """ Add variables to XMLBIF Return ------ dict: dict of type {variable: variable tags} Examples -------- {'bowel-problem': <Element VARIABLE at 0x7fe28607dd88>, 'family-out': <Element VARIABLE at 0x7fe28607de08>, 'hear-bark': <Element VARIABLE at 0x7fe28607de48>, 'dog-out': <Element VARIABLE at 0x7fe28607ddc8>, 'light-on': <Element VARIABLE at 0x7fe28607de88>} """

        variables = self.model.nodes()
        variable_tag = {}
        for var in sorted(variables):
            variable_tag[var] = etree.SubElement(self.network, "VARIABLE", attrib={'TYPE': 'nature'})
            etree.SubElement(variable_tag[var], "NAME").text = var
        return variable_tag