@Override
 public void visitPyTargetExpression(PyTargetExpression node) {
   super.visitPyTargetExpression(node);
   checkExpression(node);
 }
 @Override
 public void visitPyReferenceExpression(PyReferenceExpression node) {
   super.visitPyReferenceExpression(node);
   checkExpression(node);
 }