Python 'ast' module with Visitor pattern - get node's group, not concrete class

Question

I'm using ast python library and want to traverse through my ast nodes.

Visitor pattern is supported in the library pretty well, but if I use it, I will have to implement methods for visiting items of concrete classes, e.g. def visit_Load. In my case, concrete classes are not so important - I'd like to know whether the node is an operator or an expr according to the structure given here.

Of course, I can add generic_visit method and then check all the conditions here, but that looks like a wrong way to use the pattern.

Is there any other pretty way to implement this idea without massive code duplication?

Answer 1

This probably isn't pretty, but you can dynamically create all the methods by introspection:

def visit_expr(self, node):
    """Do something in here!"""
    self.generic_visit(node)

ExprVisitor = type('ExprVisitor', (ast.NodeVisitor,), {
    'visit_' % cls.__name__: visit_expr for cls in ast.expr.__subclasses__()})

Of course, you can keep doing this for whatever ast node types you need to deal with. . .