code: def dump_dict_of_nested_lists_to_h5(fname, data):
      
      # Open file
      print('writing to file: %s' % fname)
      f = h5py.File(fname)
      # Iterate over values
      for i, ivalue in list(data.items()):
          igrp = f.create_group(str(i))
          for j, jvalue in enumerate(ivalue):
              jgrp = igrp.create_group(str(j))
              for k, kvalue in enumerate(jvalue):
                  if kvalue.size > 0:
                      dset = jgrp.create_dataset(str(k), data=kvalue,
                                                 compression='gzip')
                  else:
                      dset = jgrp.create_dataset(str(k), data=kvalue,
                                                 maxshape=(None, ),
                                                 compression='gzip')
      # Close file
      f.close()
docs: Take nested list structure and dump it in hdf5 file.
  
  
      Parameters
      ----------
      fname : str 
          Filename
      data : dict(list(numpy.ndarray))
          Dict of nested lists with variable len arrays.
      
      
      Returns
      -------
      None