I am trying to convert ant ANTLR3 grammar to an ANTLR4 grammar, in order to use it with the antlr4-python2-runtime. This grammar is a C/C++ fuzzy parser.
After converting it (basically removing tree operators and semantic/syntactic predicates), I generated the Python2 files using:
java -jar antlr4.5-complete.jar -Dlanguage=Python2 CPPGrammar.g4
And the code is generated without any error, so I import it in my python project (I'm using PyCharm) to make some tests:
import sys, time
from antlr4 import *
from parser.CPPGrammarLexer import CPPGrammarLexer
from parser.CPPGrammarParser import CPPGrammarParser
currenttimemillis = lambda: int(round(time.time() * 1000))
def is_string(object):
return isinstance(object,str)
def parsecommandstringline(argv):
if(2!=len(argv)):
raise IndexError("Invalid args size.")
if(is_string(argv[1])):
return True
else:
raise TypeError("Argument must be str type.")
def doparsing(argv):
if parsecommandstringline(argv):
print("Arguments: OK - {0}".format(argv[1]))
input = FileStream(argv[1])
lexer = CPPGrammarLexer(input)
stream = CommonTokenStream(lexer)
parser = CPPGrammarParser(stream)
print("*** Parser: START ***")
start = currenttimemillis()
tree = parser.code()
print("*** Parser: END *** - {0} ms.".format(currenttimemillis()-start))
pass
def main(argv):
tree = doparsing(argv)
pass
if __name__ == '__main__':
main(sys.argv)
The problem is that the parsing is very slow. With a file containing ~200 lines it takes more than 5 minutes to complete, while the parsing of the same file in antlrworks only takes 1-2 seconds.
Analyzing the antlrworks tree, I noticed that the expr rule and all of its descendants are called very often and I think that I need to simplify/change these rules to make the parser operate faster:
Is my assumption correct or did I make some mistake while converting the grammar? What can be done to make parsing as fast as on antlrworks?
UPDATE:
I exported the same grammar to Java and it only took 795ms to complete the parsing. The problem seems more related to python implementation than to the grammar itself. Is there anything that can be done to speed up Python parsing?
I've read here that python can be 20-30 times slower than java, but in my case python is ~400 times slower!
antlr4-python2-runtimebecause it only takes 1 second to parse the same file on java. Python can be slower, but 400 times slower is too much to think it's a problem on my side. – Ingeborg