code: def get_db_prep_save(self, value, connection, prepared=False):
          
          log.debug("get_db_prep_save: {}, {}", value, type(value))
          if not value:
              return ''
              # For underlying (database) string types, e.g. VARCHAR, this
              # function must always return a string type.
              # https://docs.djangoproject.com/en/1.8/howto/custom-model-fields/
          return python_localized_datetime_to_human_iso(value)
docs: Convert Python value to database value for SAVING.
          We save with full timezone information.