Takes input and returns tuple of the input in canonical form (SFrame)
        along with an unpack callback function that can be applied to
        prediction results to "undo" the canonization.

def _canonize_input(self, dataset):
        """
        Takes input and returns tuple of the input in canonical form (SFrame)
        along with an unpack callback function that can be applied to
        prediction results to "undo" the canonization.
        """
        unpack = lambda x: x
        if isinstance(dataset, _tc.SArray):
            dataset = _tc.SFrame({self.feature: dataset})
        elif isinstance(dataset, _tc.Image):
            dataset = _tc.SFrame({self.feature: [dataset]})
            unpack = lambda x: x[0]
        return dataset, unpack