How to use the djangorestframework.utils.as_tuple function in djangorestframework

def _property_fields_set(self):
        """
        Returns a set containing the names of validated properties on the model.
        """
        property_fields = set(attr for attr in dir(self.model) if
                              isinstance(getattr(self.model, attr, None), property)
                              and not attr.startswith('_'))

        if self.fields:
            return property_fields & set(as_tuple(self.fields))

        return property_fields.union(set(as_tuple(self.include))) - set(as_tuple(self.exclude))

def _property_fields_set(self):
        """Returns a set containing the names of validated properties on the model."""
        resource = self.view.resource
        model = getattr(resource, 'model', None)
        fields = getattr(resource, 'fields', self.fields)
        exclude_fields = getattr(resource, 'exclude_fields', self.exclude_fields)

        property_fields = set(attr for attr in dir(model) if
                              isinstance(getattr(model, attr, None), property)
                              and not attr.startswith('_'))

        if fields:
            return property_fields & set(as_tuple(fields))

        return property_fields - set(as_tuple(exclude_fields))

def _parse(self, stream, content_type):
        """
        Parse the request content.

        May raise a 415 ErrorResponse (Unsupported Media Type), or a 400 ErrorResponse (Bad Request).
        """
        if stream is None or content_type is None:
            return (None, None)

        parsers = as_tuple(self.parsers)

        for parser_cls in parsers:
            parser = parser_cls(self)
            if parser.can_handle_request(content_type):
                return parser.parse(stream)

        raise ErrorResponse(status.HTTP_415_UNSUPPORTED_MEDIA_TYPE,
                            {'error': 'Unsupported media type in request \'%s\'.' %
                            content_type})

def _property_fields_set(self):
        """
        Returns a set containing the names of validated properties on the model.
        """
        property_fields = set(attr for attr in dir(self.model) if
                              isinstance(getattr(self.model, attr, None), property)
                              and not attr.startswith('_'))

        if self.fields:
            return property_fields & set(as_tuple(self.fields))

        return property_fields.union(set(as_tuple(self.include))) - set(as_tuple(self.exclude))

def _model_fields_set(self):
        """Return a set containing the names of validated fields on the model."""
        resource = self.view.resource
        model = getattr(resource, 'model', None)
        fields = getattr(resource, 'fields', self.fields)
        exclude_fields = getattr(resource, 'exclude_fields', self.exclude_fields)

        model_fields = set(field.name for field in model._meta.fields)

        if fields:
            return model_fields & set(as_tuple(fields))

        return model_fields - set(as_tuple(exclude_fields))

def _property_fields_set(self):
        """Returns a set containing the names of validated properties on the model."""
        resource = self.view.resource
        model = getattr(resource, 'model', None)
        fields = getattr(resource, 'fields', self.fields)
        exclude_fields = getattr(resource, 'exclude_fields', self.exclude_fields)

        property_fields = set(attr for attr in dir(model) if
                              isinstance(getattr(model, attr, None), property)
                              and not attr.startswith('_'))

        if fields:
            return property_fields & set(as_tuple(fields))

        return property_fields - set(as_tuple(exclude_fields))

def get(self, request, *args, **kwargs):
        model = self.resource.model

        queryset = self.queryset if self.queryset is not None else model.objects.all()

        if hasattr(self, 'resource'):
            ordering = getattr(self.resource, 'ordering', None)
        else:
            ordering = None

        if ordering:
            args = as_tuple(ordering)
            queryset = queryset.order_by(*args)
        return queryset.filter(**kwargs)

def _model_fields_set(self):
        """Return a set containing the names of validated fields on the model."""
        resource = self.view.resource
        model = getattr(resource, 'model', None)
        fields = getattr(resource, 'fields', self.fields)
        exclude_fields = getattr(resource, 'exclude_fields', self.exclude_fields)

        model_fields = set(field.name for field in model._meta.fields)

        if fields:
            return model_fields & set(as_tuple(fields))

        return model_fields - set(as_tuple(exclude_fields))