docs: def get_variables(self):
          """
          Add variables to PomdpX
  
          Return
          ---------------
          xml containing variables tag
          """
          state_variables = self.model['variables']['StateVar']
          for var in state_variables:
              state_var_tag = etree.SubElement(self.variable, 'StateVar', attrib={'vnamePrev': var['vnamePrev'],
                                                                                  'vnameCurr': var['vnameCurr'],
                                                                                  'fullyObs': 'true' if var['fullyObs']
                                                                                  else 'false'})
              self._add_value_enum(var, state_var_tag)
  
          obs_variables = self.model['variables']['ObsVar']
          for var in obs_variables:
              obs_var_tag = etree.SubElement(self.variable, 'ObsVar', attrib={'vname': var['vname']})
              self._add_value_enum(var, obs_var_tag)
  
          action_variables = self.model['variables']['ActionVar']
          for var in action_variables:
              action_var_tag = etree.SubElement(self.variable, 'ActionVar', attrib={'vname': var['vname']})
              self._add_value_enum(var, action_var_tag)
  
          reward_var = self.model['variables']['RewardVar']
          for var in reward_var:
              etree.SubElement(self.variable, 'RewardVar', attrib={'vname': var['vname']})
  
          return self.__str__(self.variable)[:-1]