def Copy(self, field_number=None):
    result = copy.copy(self)
    if field_number is not None:
      result.field_number = field_number
      result.CalculateTags()

    return result
Test saving does not delete unloaded values
dataset/ETHPy150Open google/grr/grr/lib/rdfvalues/structs.py/ProtoType.Copy--crossover with--dataset/ETHPy150Open duerrp/pyexperiment/tests/test_state.py/TestStateIO.test_saving_unloaded_value