code: def testStruct3(self):
      blens = [1, 2, 3]
      disps = [1, 27, 71]
      types = [MPI.INT, MPI.DOUBLE, MPI.INT]
      mt1 = MPI.Datatype.Create_struct(blens, disps, types)
      mt2 = MPI.Datatype.Create_struct([1], [0], [mt1])
      self.check(mt1)
      self.check(mt2)
      mt1.Free()
      mt2.Free()
  
imports: from mpi4py import MPI
  from mpi4py.util.dtlib import from_numpy_dtype
  from mpi4py.util.dtlib import to_numpy_dtype
  import sys, os
  import itertools
label_desc: Use image node_id 7 for calling the TestUtilDTLib obj's underlying member method code with example usage: obj.testStruct3() without return types