How to use the composeml.data_slice.extension.DataSliceContext function in composeml

def _slice_by_column(self, df):
        """Slices the data frame by an existing column."""
        slices = df.groupby(self.window_size, sort=False)
        slice_number = 1

        for group, ds in slices:
            ds = DataSliceFrame(ds)
            ds.context = DataSliceContext(
                slice_number=slice_number,
                slice_start=ds.first_valid_index(),
                slice_stop=ds.last_valid_index(),
            )
            setattr(ds.context, self.window_size, group)
            del ds.context.next_start
            slice_number += 1
            yield ds

stop = self._iloc(df.index, size.value)
        else:
            stop = start.value + size.value
            ds = df[:stop]

            # Pandas includes both endpoints when slicing by time.
            # This results in the right endpoint overlapping in consecutive data slices.
            # Resolved by making the right endpoint exclusive.
            # https://pandas.pydata.org/pandas-docs/version/0.19/gotchas.html#endpoints-are-inclusive

            if not ds.empty:
                overlap = ds.index == stop
                if overlap.any():
                    ds = ds[~overlap]

        ds.context = DataSliceContext(slice_start=start.value, slice_stop=stop)
        return ds