code: def to_ising(self):
          
          # cast to a dict
          return dict(self.spin.linear), dict(self.spin.quadratic), self.spin.offset
docs: Converts a binary quadratic model to Ising format.
  
          If the binary quadratic model's vartype is not :class:`.Vartype.SPIN`,
          values are converted.
  
          Returns:
              tuple: 3-tuple of form (`linear`, `quadratic`, `offset`), where `linear`
              is a dict of linear biases, `quadratic` is a dict of quadratic biases,
              and `offset` is a number that represents the constant offset of the
              binary quadratic model.
  
          Examples:
              This example converts a binary quadratic model to an Ising problem.
  
              >>> import dimod
              >>> model = dimod.BinaryQuadraticModel({0: 1, 1: -1, 2: .5},
              ...                                    {(0, 1): .5, (1, 2): 1.5},
              ...                                    1.4,
              ...                                    dimod.SPIN)
              >>> model.to_ising()    # doctest: +SKIP
              ({0: 1, 1: -1, 2: 0.5}, {(0, 1): 0.5, (1, 2): 1.5}, 1.4)