code: def get_begin_cursor(self, project_name, logstore_name, shard_id):
          
          return self.get_cursor(project_name, logstore_name, shard_id, "begin")
docs: Get begin cursor from log service for batch pull logs
          Unsuccessful opertaion will cause an LogException.
  
          :type project_name: string
          :param project_name: the Project name 
  
          :type logstore_name: string
          :param logstore_name: the logstore name
  
          :type shard_id: int
          :param shard_id: the shard id
  
          :return: GetLogsResponse
          
          :raise: LogException