code: def cancel(self, completed):
      self.cancel_called = True
      if completed is not self.completed:
          raise MPI.Exception(MPI.ERR_PENDING)
  
file_path: mpi4py/test/test_grequest.py
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 3 for calling the GReqCtx obj's underlying member method code with example usage: obj.cancel(completed) without return types