list(Return Values): List of the return values

def return_values(self):
        """
            list(Return Values): List of the return values
        """
        from slither.core.cfg.node import NodeType
        from slither.slithir.operations import Return
        from slither.slithir.variables import Constant

        if self._return_values is None:
            return_values = list()
            returns = [n for n in self.nodes if n.type == NodeType.RETURN]
            [return_values.extend(ir.values) for node in returns for ir in node.irs if isinstance(ir, Return)]
            self._return_values = list(set([x for x in return_values if not isinstance(x, Constant)]))
        return self._return_values