docs: def get_variables(self):
          """
          Returns a list of variables.
          Each variable is represented by an index of list.
          For example if the no of variables are 4 then the list will be
          [var_0, var_1, var_2, var_3]
  
          Returns
          -------
          list: list of variables
  
          Example
          -------
          >>> reader = UAIReader('TestUAI.uai')
          >>> reader.get_variables()
          ['var_0', 'var_1', 'var_2']
          """
          variables = []
          for var in range(0, self.no_variables):
              var_name = "var_" + str(var)
              variables.append(var_name)
          return variables