CreatePullRequestLabel.
        [Preview API] Create a label for a specified pull request. The only required field is the name of the new label.
        :param :class:`<WebApiCreateTagRequestData> <azure.devops.v5_1.git.models.WebApiCreateTagRequestData>` label: Label to assign to the 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: :class:`<WebApiTagDefinition> <azure.devops.v5_1.git.models.WebApiTagDefinition>`

def create_pull_request_label(self, label, repository_id, pull_request_id, project=None, project_id=None):
        """CreatePullRequestLabel.
        [Preview API] Create a label for a specified pull request. The only required field is the name of the new label.
        :param :class:`<WebApiCreateTagRequestData> <azure.devops.v5_1.git.models.WebApiCreateTagRequestData>` label: Label to assign to the 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: :class:`<WebApiTagDefinition> <azure.devops.v5_1.git.models.WebApiTagDefinition>`
        """
        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')
        content = self._serialize.body(label, 'WebApiCreateTagRequestData')
        response = self._send(http_method='POST',
                              location_id='f22387e3-984e-4c52-9c6d-fbb8f14c812d',
                              version='5.1-preview.1',
                              route_values=route_values,
                              query_parameters=query_parameters,
                              content=content)
        return self._deserialize('WebApiTagDefinition', response)