code: def mysum(ba, bb, dt):
      if dt is None:
          return mysum_obj(ba, bb)
      else:
          return mysum_buf(ba, bb, dt)
  
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 4 for calling a global function with example usage: mysum(ba, bb, dt) and returns: mysum_obj, mysum_buf