class_docstr: propagate exceptions to the parent's thread
  refer to https://stackoverflow.com/a/31614591/9601110
class_docstr_tok: ["propagate","exceptions","to","the","parent","'s","thread","refer","to","https",":","\/\/stackoverflow.com\/a\/31614591\/9601110"]
code: def join(self):
      super(PropagatingThread, self).join()
      if self.exc:
          raise self.exc
      return self.exc
  
file_path: byteps/launcher/launch.py
imports: from __future__ import print_function
  import os
  import re
  import subprocess
  import threading
  import sys
  import time
  from functools import reduce
label_desc: Use image node_id 3 for calling the PropagatingThread obj's underlying member method code with example usage: obj.join() and returns: self