text: """
  Provides an APIView class that is the base of all views in REST framework.
  """
  from django.conf import settings
  from django.core.exceptions import PermissionDenied
  from django.db import connections, models
  from django.http import Http404
  from django.http.response import HttpResponseBase
  from django.utils.cache import cc_delim_re, patch_vary_headers
  from django.utils.encoding import smart_str
  from django.views.decorators.csrf import csrf_exempt
  from django.views.generic import View
  
  from rest_framework import exceptions, status
  from rest_framework.request import Request
  from rest_framework.response import Response
  from rest_framework.schemas import DefaultSchema
  from rest_framework.settings import api_settings
  from rest_framework.utils import formatting
  
  
  def get_view_name(view):
      """
      Given a view instance, return a textual name to represent the view.
      This name is used in the browsable API, and in OPTIONS responses.
  
      This function is the default for the `VIEW_NAME_FUNCTION` setting.
      """
      # Name may be set by some Views, such as a ViewSet.
      name = getattr(view, 'name', None)
      if name is not None:
          return name
  
      name = view.__class__.__name__
      name = formatting.remove_trailing_string(name, 'View')
      name = formatting.remove_trailing_string(name, 'ViewSet')
      name = formatting.camelcase_to_spaces(name)
  
      # Suffix may be set by some Views, such as a ViewSet.
      suffix = getattr(view, 'suffix', None)
      if suffix:
          name += ' ' + suffix
  
      return name
  
  
  def get_view_description(view, html=False):
      """
      Given a view instance, return a textual description to represent the view.
      This name is used in the browsable API, and in OPTIONS responses.
  
      This function is the default for the `VIEW_DESCRIPTION_FUNCTION` setting.
      """
      # Description may be set by some Views, such as a ViewSet.
      description = getattr(view, 'description', None)
      if description is None:
          description = view.__class__.__doc__ or ''
  
      description = formatting.dedent(smart_str(description))
      if html:
          return formatting.markup_description(description)
      return description
  
  
  def set_rollback():
      for db in connections.all():
          if db.in_atomic_block:
              db.set_rollback(True)
  
  
  def exception_handler(exc, context):
      """
      Returns the response that should be used for any given exception.
  
      By default we handle the REST framework `APIException`, and also
      Django's built-in `Http404` and `PermissionDenied` exceptions.
  
      Any unhandled exceptions may return `None`, which will cause a 500 error
      to be raised.
      """
      if isinstance(exc, Http404):
          exc = exceptions.NotFound()
      elif isinstance(exc, PermissionDenied):
          exc = exceptions.PermissionDenied()
  
      if isinstance(exc, exceptions.APIException):
          headers = {}
          if getattr(exc, 'auth_header', None):
              headers['WWW-Authenticate'] = exc.auth_header
          if getattr(exc, 'wait', None):
              headers['Retry-After'] = '%d' % exc.wait
  
          if isinstance(exc.detail, (list, dict)):
              data = exc.detail
          else:
              data = {'detail': exc.detail}
  
          set_rollback()
          return Response(data, status=exc.status_code, headers=headers)
  
      return None
  
  
  class APIView(View):
  
      # The following policies may be set at either globally, or per-view.
      renderer_classes = api_settings.DEFAULT_RENDERER_CLASSES
      parser_classes = api_settings.DEFAULT_PARSER_CLASSES
      authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES
      throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
      permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
      content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
      metadata_class = api_settings.DEFAULT_METADATA_CLASS
      versioning_class = api_settings.DEFAULT_VERSIONING_CLASS
  
      # Allow dependency injection of other settings to make testing easier.
      settings = api_settings
  
      schema = DefaultSchema()
  
      @classmethod
      def as_view(cls, **initkwargs):
          """
          Store the original class on the view function.
  
          This allows us to discover information about the view when we do URL
          reverse lookups.  Used for breadcrumb generation.
          """
          if isinstance(getattr(cls, 'queryset', None), models.query.QuerySet):
              def force_evaluation():
                  raise RuntimeError(
                      'Do not evaluate the `.queryset` attribute directly, '
                      'as the result will be cached and reused between requests. '
                      'Use `.all()` or call `.get_queryset()` instead.'
                  )
              cls.queryset._fetch_all = force_evaluation
  
          view = super().as_view(**initkwargs)
          view.cls = cls
          view.initkwargs = initkwargs
  
          # Note: session based authentication is explicitly CSRF validated,
          # all other authentication is CSRF exempt.
          return csrf_exempt(view)
  
      @property
      def allowed_methods(self):
          """
          Wrap Django's private `_allowed_methods` interface in a public property.
          """
          return self._allowed_methods()
  
      @property
      def default_response_headers(self):
          headers = {
              'Allow': ', '.join(self.allowed_methods),
          }
          if len(self.renderer_classes) > 1:
              headers['Vary'] = 'Accept'
          return headers
  
      def http_method_not_allowed(self, request, *args, **kwargs):
          """
          If `request.method` does not correspond to a handler method,
          determine what kind of exception to raise.
          """
          raise exceptions.MethodNotAllowed(request.method)
  
      def permission_denied(self, request, message=None, code=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, code=code)
  
      def throttled(self, request, wait):
          """
          If request is throttled, determine what kind of exception to raise.
          """
          raise exceptions.Throttled(wait)
  
      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_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_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_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_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 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)
  
      # API policy instantiation methods
  
      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_renderers(self):
          """
          Instantiates and returns the list of renderers that this view can use.
          """
          return [renderer() for renderer in self.renderer_classes]
  
      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_authenticators(self):
          """
          Instantiates and returns the list of authenticators that this view can use.
          """
          return [auth() for auth in self.authentication_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_throttles(self):
          """
          Instantiates and returns the list of throttles that this view uses.
          """
          return [throttle() for throttle in self.throttle_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
  
      # API policy implementation methods
  
      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 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 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),
                      code=getattr(permission, 'code', None)
                  )
  
      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),
                      code=getattr(permission, 'code', 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)
  
      # Dispatch methods
  
      def initialize_request(self, request, *args, **kwargs):
          """
          Returns the initial request object.
          """
          parser_context = self.get_parser_context(request)
  
          return Request(
              request,
              parsers=self.get_parsers(),
              authenticators=self.get_authenticators(),
              negotiator=self.get_content_negotiator(),
              parser_context=parser_context
          )
  
      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 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 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 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
  
      # Note: Views are made CSRF exempt from within `as_view` as to prevent
      # accidental removal of this exemption in cases where `dispatch` needs to
      # be overridden.
      def dispatch(self, request, *args, **kwargs):
          """
          `.dispatch()` is pretty much the same as Django's regular dispatch,
          but with extra hooks for startup, finalize, and exception handling.
          """
          self.args = args
          self.kwargs = kwargs
          request = self.initialize_request(request, *args, **kwargs)
          self.request = request
          self.headers = self.default_response_headers  # deprecate?
  
          try:
              self.initial(request, *args, **kwargs)
  
              # Get the appropriate handler method
              if request.method.lower() in self.http_method_names:
                  handler = getattr(self, request.method.lower(),
                                    self.http_method_not_allowed)
              else:
                  handler = self.http_method_not_allowed
  
              response = handler(request, *args, **kwargs)
  
          except Exception as exc:
              response = self.handle_exception(exc)
  
          self.response = self.finalize_response(request, response, *args, **kwargs)
          return self.response
  
      def options(self, request, *args, **kwargs):
          """
          Handler method for HTTP 'OPTIONS' request.
          """
          if self.metadata_class is None:
              return self.http_method_not_allowed(request, *args, **kwargs)
          data = self.metadata_class().determine_metadata(request, self)
          return Response(data, status=status.HTTP_200_OK)
  