How to get the AST-tree instead of a list when parsing in Python with ANTLR?

Question

I get simple antlr3 grammar MicroXpath and build lexer and parser for Python.

Then I wrote a simple test code:

import antlr3 from XPathLexer import XPathLexer from XPathParser import XPathParser def print_level_order(tree, indent): print('{0}{1}'.format(' '*indent, tree.text, tree.getType())) for child in tree.getChildren(): print_level_order(child, indent+1) input = 'descendant::name[class/name[test="x"]="File"]' char_stream = antlr3.ANTLRStringStream(input) lexer = XPathLexer(char_stream) tokens = antlr3.CommonTokenStream(lexer) parser = XPathParser(tokens) tree = parser.xPath().tree print_level_order(tree, 0)

Result:

None descendant : name [ class / name [ test = "x" ] = "File" ]

Where the tree? This is a linear list! What am I doing wrong? Or using ANTLR can not build a tree?

Community · Accepted Answer · 2017-05-23 11:43:22Z

Only adding output=AST; to the options{...} is not enough: you'll have to tell ANTLR which nodes/tokens to exclude from the AST (if any), and which nodes/tokens you want to make the root of a (sub) tree. Not doing so results in a flat tree, as you already observed.

Checkout this Q&A to find out how to create a hierarchy in your tree: How to output the AST built using ANTLR?

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