3

Is it possible to do a postorder traversal on an instance of ast.NodeVisitor in Python just by manipulating the ast.NodeVisitor.generic_visit()? I did this:

class ExpParser(ast.NodeVisitor):

    def generic_visit(self, node):
        for x in ast.iter_child_nodes(node):
            ast.NodeVisitor.generic_visit(self, x)
        ast.NodeVisitor.generic_visit(self, node)

    def visit_BinOp(self, node):
        print type(node.op).__name__ 

    def visit_Name(self, node):
        print node.id

if __name__ == '__main__':
    node = ast.parse("T1+T2*T3")
    v = ExpParser()
    v.visit(node)

this gave me:

T1
T2
T3
Mult
Add

I want it to give me:

T2
T3
Mult
T1
Add

How can I do it? please I'm stuck.

Academia
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  • I notice the deprecated `compiler.visitor` package had this facility but there doesn't seem to be an equivalent in the `ast` package. – snim2 Apr 06 '12 at 12:56

1 Answers1

3

try something like this

import ast

class ExpParser(ast.NodeVisitor):

    def generic_visit(self, node):
        for field, value in reversed(list(ast.iter_fields(node))):
            if isinstance(value, list):
                for item in value:
                    if isinstance(item, ast.AST):
                        self.visit(item)
            elif isinstance(value, ast.AST):
                self.visit(value)

    def visit_BinOp(self, node):
        self.generic_visit(node)
        print type(node.op).__name__ 

    def visit_Name(self, node):
        self.generic_visit(node)
        print node.id

if __name__ == '__main__':
    node = ast.parse("T1+T2*T3")
    v = ExpParser()
    v.visit(node)

don't forget to call generic_visit on each visit method, or alternatively reimplement visit method to take care of it automatically.

Edu
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