How to use the plonk.snap.snap.SubSnap function in plonk

def _getitem(
        self, inp: Union[str, ndarray, int, slice], sinks: bool = False,
    ) -> Union[ndarray, SubSnap]:
        """Return an array, or family, or subset."""
        if isinstance(inp, str):
            return self._getitem_from_str(inp, sinks)
        if sinks:
            raise ValueError('Cannot return sinks as SubSnap')
        if isinstance(inp, ndarray):
            if np.issubdtype(np.bool, inp.dtype):
                return SubSnap(self, np.flatnonzero(inp))
            if np.issubdtype(np.int, inp.dtype):
                return SubSnap(self, inp)
        if isinstance(inp, int):
            return SubSnap(self, np.array([inp]))
        if isinstance(inp, slice):
            i1, i2, step = inp.start, inp.stop, inp.step
            if i1 is None:
                i1 = 0
            if i2 is None:
                i2 = len(self)
            if step is not None:
                return SubSnap(self, np.arange(i1, i2, step))
            return SubSnap(self, np.arange(i1, i2))
        if self._extra_quantities:
            raise ValueError('Cannot determine item to return.')
        raise ValueError(
            'Cannot determine item to return. Extra quantities are available via\n'
            'snap.extra_quantities().'

def _get_family_subsnap(self, name: str):
        """Get a family by name."""
        if name in self._families:
            if self._families[name] is None:
                ind = self.particle_indices(name)
                if len(ind) == 0:
                    raise ValueError(f'No {name} particles available')
                self._families[name] = ind
            ind = self._families[name]
            if isinstance(ind, list):
                return [SubSnap(self, _ind) for _ind in ind]
            return SubSnap(self, ind)
        raise ValueError('Family not available')

def _get_family_subsnap(self, name: str):
        """Get a family by name."""
        if name in self._families:
            if self._families[name] is None:
                ind = self.particle_indices(name)
                if len(ind) == 0:
                    raise ValueError(f'No {name} particles available')
                self._families[name] = ind
            ind = self._families[name]
            if isinstance(ind, list):
                return [SubSnap(self, _ind) for _ind in ind]
            return SubSnap(self, ind)
        raise ValueError('Family not available')

if isinstance(inp, ndarray):
            if np.issubdtype(np.bool, inp.dtype):
                return SubSnap(self, np.flatnonzero(inp))
            if np.issubdtype(np.int, inp.dtype):
                return SubSnap(self, inp)
        if isinstance(inp, int):
            return SubSnap(self, np.array([inp]))
        if isinstance(inp, slice):
            i1, i2, step = inp.start, inp.stop, inp.step
            if i1 is None:
                i1 = 0
            if i2 is None:
                i2 = len(self)
            if step is not None:
                return SubSnap(self, np.arange(i1, i2, step))
            return SubSnap(self, np.arange(i1, i2))
        if self._extra_quantities:
            raise ValueError('Cannot determine item to return.')
        raise ValueError(
            'Cannot determine item to return. Extra quantities are available via\n'
            'snap.extra_quantities().'

def _getitem(
        self, inp: Union[str, ndarray, int, slice], sinks: bool = False,
    ) -> Union[ndarray, SubSnap]:
        """Return an array, or family, or subset."""
        if isinstance(inp, str):
            return self._getitem_from_str(inp, sinks)
        if sinks:
            raise ValueError('Cannot return sinks as SubSnap')
        if isinstance(inp, ndarray):
            if np.issubdtype(np.bool, inp.dtype):
                return SubSnap(self, np.flatnonzero(inp))
            if np.issubdtype(np.int, inp.dtype):
                return SubSnap(self, inp)
        if isinstance(inp, int):
            return SubSnap(self, np.array([inp]))
        if isinstance(inp, slice):
            i1, i2, step = inp.start, inp.stop, inp.step
            if i1 is None:
                i1 = 0
            if i2 is None:
                i2 = len(self)
            if step is not None:
                return SubSnap(self, np.arange(i1, i2, step))
            return SubSnap(self, np.arange(i1, i2))
        if self._extra_quantities:
            raise ValueError('Cannot determine item to return.')
        raise ValueError(
            'Cannot determine item to return. Extra quantities are available via\n'
            'snap.extra_quantities().'