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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_default(self):
 """ ``True`` if values of all config items in this section and its subsections have their values equal to defaults or have no value set. """

        for _, item in self.iter_items(recursive=True):
            if not item.is_default:
                return False
        return True