code: def get_pull_request_labels(self, repository_id, pull_request_id, project=None, project_id=None):
          
          route_values = {}
          if project is not None:
              route_values['project'] = self._serialize.url('project', project, 'str')
          if repository_id is not None:
              route_values['repositoryId'] = self._serialize.url('repository_id', repository_id, 'str')
          if pull_request_id is not None:
              route_values['pullRequestId'] = self._serialize.url('pull_request_id', pull_request_id, 'int')
          query_parameters = {}
          if project_id is not None:
              query_parameters['projectId'] = self._serialize.query('project_id', project_id, 'str')
          response = self._send(http_method='GET',
                                location_id='f22387e3-984e-4c52-9c6d-fbb8f14c812d',
                                version='5.0-preview.1',
                                route_values=route_values,
                                query_parameters=query_parameters)
          return self._deserialize('[WebApiTagDefinition]', self._unwrap_collection(response))
docs: GetPullRequestLabels.
          [Preview API] Get all the labels assigned to a pull request.
          :param str repository_id: The repository ID of the pull request’s target branch.
          :param int pull_request_id: ID of the pull request.
          :param str project: Project ID or project name
          :param str project_id: Project ID or project name.
          :rtype: [WebApiTagDefinition]