class ViewSet

    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 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_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_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_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 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 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)