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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 default_attributes(self):
 """List of default attributes for the dataset."""

        if self._default_attributes is None:
            self._default_attributes = {
                name: attr
                for name, attr in self.attributes.items()
                if attr.default is True
            }
        return self._default_attributes