IronPython.Compiler.Ast.TupleExpression.CheckAssign C# (CSharp) Method

        internal override string CheckAssign() {
            if (Items.Count == 0) {
                return "can't assign to ()";
            }
            for (int i = 0; i < Items.Count; i++) {
                Expression e = Items[i];
                if (e.CheckAssign() != null) {
                    // we don't return the same message here as CPython doesn't seem to either, 
                    // for example ((yield a), 2,3) = (2,3,4) gives a different error than
                    // a = yield 3 = yield 4.
                    return "can't assign to " + e.NodeName;
                }
            }
            return null;
        }