How to use the stonesoup.types.state.StateMutableSequence function in stonesoup

if isinstance(index, slice) and (
                isinstance(index.start, datetime.datetime)
                or isinstance(index.stop, datetime.datetime)):
            items = []
            for state in self.states:
                try:
                    if index.start and state.timestamp < index.start:
                        continue
                    if index.stop and state.timestamp >= index.stop:
                        continue
                except TypeError as exc:
                    raise TypeError(
                        'both indices must be `datetime.datetime` objects for'
                        'time slice') from exc
                items.append(state)
            return StateMutableSequence(items[::index.step])
        elif isinstance(index, datetime.datetime):
            for state in self.states:
                if state.timestamp == index:
                    return state
            else:
                raise IndexError('timestamp not found in states')
        elif isinstance(index, slice):
            return StateMutableSequence(self.states.__getitem__(index))
        else:
            return self.states.__getitem__(index)

"""
        Extracts a list of :class:`~states` from a list of (or single) objects
        containing states. This method is defined to handle :class:`~track`,
        :class:`~groundtruthpath` and :class:`~detection` objects

        Parameters
        ----------
        object_with_states: object containing a list of states
            Method of state extraction depends on the type of the object

        Returns
        -------
        : list of :class:`~.State`
        """

        state_list = StateMutableSequence()
        for element in list(object_with_states):
            if isinstance(element, StateMutableSequence):
                state_list.extend(element.states)
            elif isinstance(element, State):
                state_list.append(element)
            else:
                raise ValueError(
                    "{!r} has no state extraction method".format(element))

        return state_list

# -*- coding: utf-8 -*-
import uuid

from ..base import Property
from .multihypothesis import MultipleHypothesis
from .state import State, StateMutableSequence
from .update import Update


class Track(StateMutableSequence):
    """Track type

    A :class:`~.StateMutableSequence` representing a track.
    """

    states = Property(
        [State],
        default=None,
        doc="The initial states of the track. Default `None` which initialises"
            "with empty list.")

    id = Property(
        str,
        default=None,
        doc="The unique track ID")

from ..base import Property
from .state import State, StateMutableSequence


class GroundTruthState(State):
    """Ground Truth State type"""
    metadata = Property(dict, default=None,
                        doc='Dictionary of metadata items for Detections.')

    def __init__(self, state_vector, *args, **kwargs):
        super().__init__(state_vector, *args, **kwargs)
        if self.metadata is None:
            self.metadata = {}


class GroundTruthPath(StateMutableSequence):
    """Ground Truth Path type

    A :class:`~.StateMutableSequence` representing a track.
    """

    states = Property(
        [GroundTruthState],
        default=None,
        doc="List of groundtruth states to initialise path with. Default "
            "`None` which initialises with an empty list.")

containing states. This method is defined to handle :class:`~track`,
        :class:`~groundtruthpath` and :class:`~detection` objects

        Parameters
        ----------
        object_with_states: object containing a list of states
            Method of state extraction depends on the type of the object

        Returns
        -------
        : list of :class:`~.State`
        """

        state_list = StateMutableSequence()
        for element in list(object_with_states):
            if isinstance(element, StateMutableSequence):
                state_list.extend(element.states)
            elif isinstance(element, State):
                state_list.append(element)
            else:
                raise ValueError(
                    "{!r} has no state extraction method".format(element))

        return state_list