def _register_expr(self, s):
        if not is_legal_name(s):
            expr = ExprEvaluator(s)
            if self._exprs is None:
                self._exprs = {}
            self._exprs[s] = expr
If the given string contains an expression, create an ExprEvaluator
dataset/ETHPy150Open OpenMDAO/OpenMDAO-Framework/openmdao.main/src/openmdao/main/case.py/Case._register_expr