class ReadOnlyModelViewSet

    def _allowed_methods(self):
        return [m.upper() for m in self.http_method_names if hasattr(self, m)]

    def check_object_permissions(self, request, obj):
        """
        Check if the request should be permitted for a given object.
        Raises an appropriate exception if the request is not permitted.
        """
        for permission in self.get_permissions():
            if not permission.has_object_permission(request, self, obj):
                self.permission_denied(
                    request, message=getattr(permission, 'message', None)
                )

    def check_permissions(self, request):
        """
        Check if the request should be permitted.
        Raises an appropriate exception if the request is not permitted.
        """
        for permission in self.get_permissions():
            if not permission.has_permission(request, self):
                self.permission_denied(
                    request, message=getattr(permission, 'message', None)
                )

    def check_throttles(self, request):
        """
        Check if request should be throttled.
        Raises an appropriate exception if the request is throttled.
        """
        throttle_durations = []
        for throttle in self.get_throttles():
            if not throttle.allow_request(request, self):
                throttle_durations.append(throttle.wait())

        if throttle_durations:
            # Filter out `None` values which may happen in case of config / rate
            # changes, see #1438
            durations = [
                duration for duration in throttle_durations
                if duration is not None
            ]

            duration = max(durations, default=None)
            self.throttled(request, duration)

    def determine_version(self, request, *args, **kwargs):
        """
        If versioning is being used, then determine any API version for the
        incoming request. Returns a two-tuple of (version, versioning_scheme)
        """
        if self.versioning_class is None:
            return (None, None)
        scheme = self.versioning_class()
        return (scheme.determine_version(request, *args, **kwargs), scheme)

    def filter_queryset(self, queryset):
        """
        Given a queryset, filter it with whichever filter backend is in use.

        You are unlikely to want to override this method, although you may need
        to call it either from a list view, or from a custom `get_object`
        method if you want to apply the configured filtering backend to the
        default queryset.
        """
        for backend in list(self.filter_backends):
            queryset = backend().filter_queryset(self.request, queryset, self)
        return queryset

    def finalize_response(self, request, response, *args, **kwargs):
        """
        Returns the final response object.
        """
        # Make the error obvious if a proper response is not returned
        assert isinstance(response, HttpResponseBase), (
            'Expected a `Response`, `HttpResponse` or `HttpStreamingResponse` '
            'to be returned from the view, but received a `%s`'
            % type(response)
        )

        if isinstance(response, Response):
            if not getattr(request, 'accepted_renderer', None):
                neg = self.perform_content_negotiation(request, force=True)
                request.accepted_renderer, request.accepted_media_type = neg

            response.accepted_renderer = request.accepted_renderer
            response.accepted_media_type = request.accepted_media_type
            response.renderer_context = self.get_renderer_context()

        # Add new vary headers to the response instead of overwriting.
        vary_headers = self.headers.pop('Vary', None)
        if vary_headers is not None:
            patch_vary_headers(response, cc_delim_re.split(vary_headers))

        for key, value in self.headers.items():
            response[key] = value

        return response

    def get_authenticate_header(self, request):
        """
        If a request is unauthenticated, determine the WWW-Authenticate
        header to use for 401 responses, if any.
        """
        authenticators = self.get_authenticators()
        if authenticators:
            return authenticators[0].authenticate_header(request)

    def get_authenticators(self):
        """
        Instantiates and returns the list of authenticators that this view can use.
        """
        return [auth() for auth in self.authentication_classes]

    def get_content_negotiator(self):
        """
        Instantiate and return the content negotiation class to use.
        """
        if not getattr(self, '_negotiator', None):
            self._negotiator = self.content_negotiation_class()
        return self._negotiator

    def get_exception_handler(self):
        """
        Returns the exception handler that this view uses.
        """
        return self.settings.EXCEPTION_HANDLER

    def get_exception_handler_context(self):
        """
        Returns a dict that is passed through to EXCEPTION_HANDLER,
        as the `context` argument.
        """
        return {
            'view': self,
            'args': getattr(self, 'args', ()),
            'kwargs': getattr(self, 'kwargs', {}),
            'request': getattr(self, 'request', None)
        }

    def get_extra_action_url_map(self):
        """
        Build a map of {names: urls} for the extra actions.

        This method will noop if `detail` was not provided as a view initkwarg.
        """
        action_urls = OrderedDict()

        # exit early if `detail` has not been provided
        if self.detail is None:
            return action_urls

        # filter for the relevant extra actions
        actions = [
            action for action in self.get_extra_actions()
            if action.detail == self.detail
        ]

        for action in actions:
            try:
                url_name = '%s-%s' % (self.basename, action.url_name)
                url = reverse(url_name, self.args, self.kwargs, request=self.request)
                view = self.__class__(**action.kwargs)
                action_urls[view.get_view_name()] = url
            except NoReverseMatch:
                pass  # URL requires additional arguments, ignore

        return action_urls

    @classmethod
    def get_extra_actions(cls):
        """
        Get the methods that are marked as an extra ViewSet `@action`.
        """
        return [method for _, method in getmembers(cls, _is_extra_action)]

    def get_format_suffix(self, **kwargs):
        """
        Determine if the request includes a '.json' style format suffix
        """
        if self.settings.FORMAT_SUFFIX_KWARG:
            return kwargs.get(self.settings.FORMAT_SUFFIX_KWARG)

    def get_object(self):
        """
        Returns the object the view is displaying.

        You may want to override this if you need to provide non-standard
        queryset lookups.  Eg if objects are referenced using multiple
        keyword arguments in the url conf.
        """
        queryset = self.filter_queryset(self.get_queryset())

        # Perform the lookup filtering.
        lookup_url_kwarg = self.lookup_url_kwarg or self.lookup_field

        assert lookup_url_kwarg in self.kwargs, (
            'Expected view %s to be called with a URL keyword argument '
            'named "%s". Fix your URL conf, or set the `.lookup_field` '
            'attribute on the view correctly.' %
            (self.__class__.__name__, lookup_url_kwarg)
        )

        filter_kwargs = {self.lookup_field: self.kwargs[lookup_url_kwarg]}
        obj = get_object_or_404(queryset, **filter_kwargs)

        # May raise a permission denied
        self.check_object_permissions(self.request, obj)

        return obj

    def get_paginated_response(self, data):
        """
        Return a paginated style `Response` object for the given output data.
        """
        assert self.paginator is not None
        return self.paginator.get_paginated_response(data)

    def get_parser_context(self, http_request):
        """
        Returns a dict that is passed through to Parser.parse(),
        as the `parser_context` keyword argument.
        """
        # Note: Additionally `request` and `encoding` will also be added
        #       to the context by the Request object.
        return {
            'view': self,
            'args': getattr(self, 'args', ()),
            'kwargs': getattr(self, 'kwargs', {})
        }

    def get_parsers(self):
        """
        Instantiates and returns the list of parsers that this view can use.
        """
        return [parser() for parser in self.parser_classes]

    def get_permissions(self):
        """
        Instantiates and returns the list of permissions that this view requires.
        """
        return [permission() for permission in self.permission_classes]

    def get_queryset(self):
        """
        Get the list of items for this view.
        This must be an iterable, and may be a queryset.
        Defaults to using `self.queryset`.

        This method should always be used rather than accessing `self.queryset`
        directly, as `self.queryset` gets evaluated only once, and those results
        are cached for all subsequent requests.

        You may want to override this if you need to provide different
        querysets depending on the incoming request.

        (Eg. return a list of items that is specific to the user)
        """
        assert self.queryset is not None, (
            "'%s' should either include a `queryset` attribute, "
            "or override the `get_queryset()` method."
            % self.__class__.__name__
        )

        queryset = self.queryset
        if isinstance(queryset, QuerySet):
            # Ensure queryset is re-evaluated on each request.
            queryset = queryset.all()
        return queryset

    def get_renderer_context(self):
        """
        Returns a dict that is passed through to Renderer.render(),
        as the `renderer_context` keyword argument.
        """
        # Note: Additionally 'response' will also be added to the context,
        #       by the Response object.
        return {
            'view': self,
            'args': getattr(self, 'args', ()),
            'kwargs': getattr(self, 'kwargs', {}),
            'request': getattr(self, 'request', None)
        }

    def get_renderers(self):
        """
        Instantiates and returns the list of renderers that this view can use.
        """
        return [renderer() for renderer in self.renderer_classes]

    def get_serializer(self, *args, **kwargs):
        """
        Return the serializer instance that should be used for validating and
        deserializing input, and for serializing output.
        """
        serializer_class = self.get_serializer_class()
        kwargs['context'] = self.get_serializer_context()
        return serializer_class(*args, **kwargs)

    def get_serializer_class(self):
        """
        Return the class to use for the serializer.
        Defaults to using `self.serializer_class`.

        You may want to override this if you need to provide different
        serializations depending on the incoming request.

        (Eg. admins get full serialization, others get basic serialization)
        """
        assert self.serializer_class is not None, (
            "'%s' should either include a `serializer_class` attribute, "
            "or override the `get_serializer_class()` method."
            % self.__class__.__name__
        )

        return self.serializer_class

    def get_serializer_context(self):
        """
        Extra context provided to the serializer class.
        """
        return {
            'request': self.request,
            'format': self.format_kwarg,
            'view': self
        }

    def get_throttles(self):
        """
        Instantiates and returns the list of throttles that this view uses.
        """
        return [throttle() for throttle in self.throttle_classes]

    def get_view_description(self, html=False):
        """
        Return some descriptive text for the view, as used in OPTIONS responses
        and in the browsable API.
        """
        func = self.settings.VIEW_DESCRIPTION_FUNCTION
        return func(self, html)

    def get_view_name(self):
        """
        Return the view name, as used in OPTIONS responses and in the
        browsable API.
        """
        func = self.settings.VIEW_NAME_FUNCTION
        return func(self)

    def handle_exception(self, exc):
        """
        Handle any exception that occurs, by returning an appropriate response,
        or re-raising the error.
        """
        if isinstance(exc, (exceptions.NotAuthenticated,
                            exceptions.AuthenticationFailed)):
            # WWW-Authenticate header for 401 responses, else coerce to 403
            auth_header = self.get_authenticate_header(self.request)

            if auth_header:
                exc.auth_header = auth_header
            else:
                exc.status_code = status.HTTP_403_FORBIDDEN

        exception_handler = self.get_exception_handler()

        context = self.get_exception_handler_context()
        response = exception_handler(exc, context)

        if response is None:
            self.raise_uncaught_exception(exc)

        response.exception = True
        return response

    def initial(self, request, *args, **kwargs):
        """
        Runs anything that needs to occur prior to calling the method handler.
        """
        self.format_kwarg = self.get_format_suffix(**kwargs)

        # Perform content negotiation and store the accepted info on the request
        neg = self.perform_content_negotiation(request)
        request.accepted_renderer, request.accepted_media_type = neg

        # Determine the API version, if versioning is in use.
        version, scheme = self.determine_version(request, *args, **kwargs)
        request.version, request.versioning_scheme = version, scheme

        # Ensure that the incoming request is permitted
        self.perform_authentication(request)
        self.check_permissions(request)
        self.check_throttles(request)

    def list(self, request, *args, **kwargs):
        queryset = self.filter_queryset(self.get_queryset())

        page = self.paginate_queryset(queryset)
        if page is not None:
            serializer = self.get_serializer(page, many=True)
            return self.get_paginated_response(serializer.data)

        serializer = self.get_serializer(queryset, many=True)
        return Response(serializer.data)

    def paginate_queryset(self, queryset):
        """
        Return a single page of results, or `None` if pagination is disabled.
        """
        if self.paginator is None:
            return None
        return self.paginator.paginate_queryset(queryset, self.request, view=self)

    def perform_authentication(self, request):
        """
        Perform authentication on the incoming request.

        Note that if you override this and simply 'pass', then authentication
        will instead be performed lazily, the first time either
        `request.user` or `request.auth` is accessed.
        """
        request.user

    def perform_content_negotiation(self, request, force=False):
        """
        Determine which renderer and media type to use render the response.
        """
        renderers = self.get_renderers()
        conneg = self.get_content_negotiator()

        try:
            return conneg.select_renderer(request, renderers, self.format_kwarg)
        except Exception:
            if force:
                return (renderers[0], renderers[0].media_type)
            raise

    def permission_denied(self, request, message=None):
        """
        If request is not permitted, determine what kind of exception to raise.
        """
        if request.authenticators and not request.successful_authenticator:
            raise exceptions.NotAuthenticated()
        raise exceptions.PermissionDenied(detail=message)

    def raise_uncaught_exception(self, exc):
        if settings.DEBUG:
            request = self.request
            renderer_format = getattr(request.accepted_renderer, 'format')
            use_plaintext_traceback = renderer_format not in ('html', 'api', 'admin')
            request.force_plaintext_errors(use_plaintext_traceback)
        raise exc

    def retrieve(self, request, *args, **kwargs):
        instance = self.get_object()
        serializer = self.get_serializer(instance)
        return Response(serializer.data)

    def reverse_action(self, url_name, *args, **kwargs):
        """
        Reverse the action for the given `url_name`.
        """
        url_name = '%s-%s' % (self.basename, url_name)
        kwargs.setdefault('request', self.request)

        return reverse(url_name, *args, **kwargs)

    def setup(self, request, *args, **kwargs):
        """Initialize attributes shared by all view methods."""
        if hasattr(self, 'get') and not hasattr(self, 'head'):
            self.head = self.get
        self.request = request
        self.args = args
        self.kwargs = kwargs

    def throttled(self, request, wait):
        """
        If request is throttled, determine what kind of exception to raise.
        """
        raise exceptions.Throttled(wait)