code: def write(filename, groupname, items, times, features, properties=None,
            dformat='dense', chunk_size='auto', sparsity=0.1, mode='a'):
      sparsity = sparsity if dformat == 'sparse' else None
      data = Data(items, times, features, properties=properties,
                  sparsity=sparsity, check=True)
      Writer(filename, chunk_size=chunk_size).write(data, groupname, append=True)