visitors.py

import ast

class PLPostorderVisitor():
    def visit(self, node, config=None):
        """Visit a node."""
        if node == None:
            return None
        # visit children first
        for field, value in ast.iter_fields(node):
            if isinstance(value, list):
                for item in value:
                    if isinstance(item, ast.AST):
                        self.visit(item, config)
            elif isinstance(value, ast.AST):
                self.visit(value, config)
        # visit current node after visiting children (postorder)
        method = 'visit_' + node.__class__.__name__
        visitor = getattr(self, method, self.generic_visit)
        visit_return = visitor(node, config)
        if config == "DEBUG" and hasattr(node, "pl_data"):
            print(node.__class__.__name__+": ", node.pl_data)
        return visit_return

    def generic_visit(self, node, config=None):
        """Called if no explicit visitor function exists for a node."""
        pass

class PLPreorderVisitor():
    def visit(self, node, config=None):
        """Visit a node."""
        if node == None:
            return None
        method = 'visit_' + node.__class__.__name__
        visitor = getattr(self, method, self.generic_visit)
        visit_return = visitor(node, config)

        # visit children nodes
        for field, value in ast.iter_fields(node):
            if isinstance(value, list):
                for item in value:
                    if isinstance(item, ast.AST):
                        self.visit(item, config)
            elif isinstance(value, ast.AST):
                self.visit(value, config)
        return visit_return

    def generic_visit(self, node, config=None):
        """Called if no explicit visitor function exists for a node."""
        pass