validate_expr(expr_ty exp, expr_context_ty ctx)
{
    int check_ctx = 1;
    expr_context_ty actual_ctx;

    /* First check expression context. */
    switch (exp->kind) {
    case Attribute_kind:
        actual_ctx = exp->v.Attribute.ctx;
        break;
    case Subscript_kind:
        actual_ctx = exp->v.Subscript.ctx;
        break;
    case Starred_kind:
        actual_ctx = exp->v.Starred.ctx;
        break;
    case Name_kind:
        actual_ctx = exp->v.Name.ctx;
        break;
    case List_kind:
        actual_ctx = exp->v.List.ctx;
        break;
    case Tuple_kind:
        actual_ctx = exp->v.Tuple.ctx;
        break;
    default:
        if (ctx != Load) {
            PyErr_Format(PyExc_ValueError, "expression which can't be "
                         "assigned to in %s context", expr_context_name(ctx));
            return 0;
        }
        check_ctx = 0;
        /* set actual_ctx to prevent gcc warning */
        actual_ctx = 0;
    }
    if (check_ctx && actual_ctx != ctx) {
        PyErr_Format(PyExc_ValueError, "expression must have %s context but has %s instead",
                     expr_context_name(ctx), expr_context_name(actual_ctx));
        return 0;
    }

    /* Now validate expression. */
    switch (exp->kind) {
    case BoolOp_kind:
        if (asdl_seq_LEN(exp->v.BoolOp.values) < 2) {
            PyErr_SetString(PyExc_ValueError, "BoolOp with less than 2 values");
            return 0;
        }
        return validate_exprs(exp->v.BoolOp.values, Load, 0);
    case BinOp_kind:
        return validate_expr(exp->v.BinOp.left, Load) &&
            validate_expr(exp->v.BinOp.right, Load);
    case UnaryOp_kind:
        return validate_expr(exp->v.UnaryOp.operand, Load);
    case Lambda_kind:
        return validate_arguments(exp->v.Lambda.args) &&
            validate_expr(exp->v.Lambda.body, Load);
    case IfExp_kind:
        return validate_expr(exp->v.IfExp.test, Load) &&
            validate_expr(exp->v.IfExp.body, Load) &&
            validate_expr(exp->v.IfExp.orelse, Load);
    case Dict_kind:
        if (asdl_seq_LEN(exp->v.Dict.keys) != asdl_seq_LEN(exp->v.Dict.values)) {
            PyErr_SetString(PyExc_ValueError,
                            "Dict doesn't have the same number of keys as values");
            return 0;
        }
        /* null_ok=1 for keys expressions to allow dict unpacking to work in
           dict literals, i.e. ``{**{a:b}}`` */
        return validate_exprs(exp->v.Dict.keys, Load, /*null_ok=*/ 1) &&
            validate_exprs(exp->v.Dict.values, Load, /*null_ok=*/ 0);
    case Set_kind:
        return validate_exprs(exp->v.Set.elts, Load, 0);
#define COMP(NAME) \
        case NAME ## _kind: \
            return validate_comprehension(exp->v.NAME.generators) && \
                validate_expr(exp->v.NAME.elt, Load);
    COMP(ListComp)
    COMP(SetComp)
    COMP(GeneratorExp)
#undef COMP
    case DictComp_kind:
        return validate_comprehension(exp->v.DictComp.generators) &&
            validate_expr(exp->v.DictComp.key, Load) &&
            validate_expr(exp->v.DictComp.value, Load);
    case Yield_kind:
        return !exp->v.Yield.value || validate_expr(exp->v.Yield.value, Load);
    case YieldFrom_kind:
        return validate_expr(exp->v.YieldFrom.value, Load);
    case Await_kind:
        return validate_expr(exp->v.Await.value, Load);
    case Compare_kind:
        if (!asdl_seq_LEN(exp->v.Compare.comparators)) {
            PyErr_SetString(PyExc_ValueError, "Compare with no comparators");
            return 0;
        }
        if (asdl_seq_LEN(exp->v.Compare.comparators) !=
            asdl_seq_LEN(exp->v.Compare.ops)) {
            PyErr_SetString(PyExc_ValueError, "Compare has a different number "
                            "of comparators and operands");
            return 0;
        }
        return validate_exprs(exp->v.Compare.comparators, Load, 0) &&
            validate_expr(exp->v.Compare.left, Load);
    case Call_kind:
        return validate_expr(exp->v.Call.func, Load) &&
            validate_exprs(exp->v.Call.args, Load, 0) &&
            validate_keywords(exp->v.Call.keywords);
    case Constant_kind:
        if (!validate_constant(exp->v.Constant.value)) {
            PyErr_Format(PyExc_TypeError,
                         "got an invalid type in Constant: %s",
                         Py_TYPE(exp->v.Constant.value)->tp_name);
            return 0;
        }
        return 1;
    case JoinedStr_kind:
        return validate_exprs(exp->v.JoinedStr.values, Load, 0);
    case FormattedValue_kind:
        if (validate_expr(exp->v.FormattedValue.value, Load) == 0)
            return 0;
        if (exp->v.FormattedValue.format_spec)
            return validate_expr(exp->v.FormattedValue.format_spec, Load);
        return 1;
    case Attribute_kind:
        return validate_expr(exp->v.Attribute.value, Load);
    case Subscript_kind:
        return validate_slice(exp->v.Subscript.slice) &&
            validate_expr(exp->v.Subscript.value, Load);
    case Starred_kind:
        return validate_expr(exp->v.Starred.value, ctx);
    case List_kind:
        return validate_exprs(exp->v.List.elts, ctx, 0);
    case Tuple_kind:
        return validate_exprs(exp->v.Tuple.elts, ctx, 0);
    /* This last case doesn't have any checking. */
    case Name_kind:
        return 1;
    default:
        PyErr_SetString(PyExc_SystemError, "unexpected expression");
        return 0;
    }
}
Unknown