How to parse tree using python2 runtime with antlr4
I am trying to use antlr4 version 4.4 and python2 runtime . Grammar from antlr4 book, page 6, file: Hello.g4:
grammar Hello;
r : 'hello' ID ;
ID : [a-z]+ ;
WS : [ \t\r\n]+ -> skip ;
and i create lexer and parser with command
antlr4 -Dlanguage=Python2 Hello.g4
then the files HelloLexer.py, HelloParser.py and HelloListener.py are generated. I am doing a main program test.py to test the generated python parser:
from antlr4 import *
from HelloLexer import HelloLexer
from HelloParser import HelloParser
def main(argv):
input = FileStream(argv[1])
lexer = HelloLexer(input)
stream = CommonTokenStream(lexer)
parser = HelloParser(stream)
tree = parser.r()
print tree.toStringTree(parser) <= the problem is here!
if __name__ == '__main__':
import sys
main(sys.argv)
Everything works fine except that I cannot print the parse tree.
C:\Users\LG\antlr\tpantlr2-code\code\install>Test.py data.txt
Traceback (most recent call last):
File "C:\Users\LG\antlr\tpantlr2-code\code\install\Test.py", line 15, in <module>
main(sys.argv)
File "C:\Users\LG\antlr\tpantlr2-code\code\install\Test.py", line 11, in main
print tree.toStringTree(parser)
File "C:\Python27\lib\site-packages\antlr4\RuleContext.py", line 181, in toStringTree
return Trees.toStringTree(self, ruleNames=ruleNames, recog=recog)
File "C:\Python27\lib\site-packages\antlr4\tree\Trees.py", line 48, in toStringTree
s = escapeWhitespace(cls.getNodeText(t, ruleNames), False)
File "C:\Python27\lib\site-packages\antlr4\tree\Trees.py", line 68, in getNodeText
return ruleNames[t.getRuleContext().getRuleIndex()]
TypeError: 'HelloParser' object does not support indexing
I haven't figured out what the problem is yet.
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2 answers
Oddly enough, toStringTree is a class method at runtime Python. You can call it like this to get a lisp style parse tree including string tokens:
from antlr4 import *
from antlr4.tree.Trees import Trees
# import your parser & lexer here
# setup your lexer, stream, parser and tree like normal
print(Trees.toStringTree(tree, None, parser))
# the None is an optional rule names list
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