class_docstr: tracker for rabit
class_docstr_tok: ["tracker","for","rabit"]
code: def get_neighbor(rank, nslave):
      rank = rank + 1
      ret = []
      if rank > 1:
          ret.append(rank // 2 - 1)
      if rank * 2 - 1 < nslave:
          ret.append(rank * 2 - 1)
      if rank * 2 < nslave:
          ret.append(rank * 2)
      return ret
  
imports: from __future__ import absolute_import
  import os
  import sys
  import socket
  import struct
  import subprocess
  import argparse
  import time
  import logging
  from threading import Thread
label_desc: Use image node_id 3 for calling the RabitTracker obj's underlying member method code with example usage: obj.get_neighbor(rank, nslave) and returns: ret