def default_group_slice(self):
        """The default group slice of the dataset, or None if the dataset is
        not grouped.

        Examples::

            import fiftyone as fo
            import fiftyone.zoo as foz

            dataset = foz.load_zoo_dataset("quickstart-groups")

            print(dataset.default_group_slice)
            # left

            # Change the default group slice
            dataset.default_group_slice = "right"

            print(dataset.default_group_slice)
            # right
        """
        if self.media_type != fom.GROUP:
            return None

        return self._doc.default_group_slice
The default group slice of the dataset, or None if the dataset is
        not grouped.

        Examples::

            import fiftyone as fo
            import fiftyone.zoo as foz

            dataset = foz.load_zoo_dataset("quickstart-groups")

            print(dataset.default_group_slice)
            # left

            # Change the default group slice
            dataset.default_group_slice = "right"

            print(dataset.default_group_slice)
            # right
        
fiftyone/core/dataset.py