Evaluate the content type for the response to a client ``request``.

        The method uses the :attr:`response_content_types` parameter of
        accepted content types and the content types accepted by the client
        ``request`` and figures out the best match.

def set_response_content_type(self, response_content_types=None):
        '''Evaluate the content type for the response to a client ``request``.

        The method uses the :attr:`response_content_types` parameter of
        accepted content types and the content types accepted by the client
        ``request`` and figures out the best match.
        '''
        request_content_types = self.content_types
        if request_content_types:
            ct = request_content_types.best_match(response_content_types)
            if ct and '*' in ct:
                ct = None
            if not ct and response_content_types:
                raise HttpException(status=415, msg=request_content_types)
            self.response.content_type = ct