Parsing large files using ANTLR4 in Python

ANTLR4 is a powerful parsing tool that can be used to parse big files in Python. The ANTLR4 tool generates parsers from grammars defined in a language-independent way, so it can be used to parse many different programming languages.

To use ANTLR4 in Python, we first need to install the ANTLR4 Python runtime library. We can do this using pip:

Copy codepip install antlr4-python3-runtime

Once we have installed the ANTLR4 Python runtime, we can start using it to parse big files. To do this, we need to define a grammar that describes the structure of the file we want to parse.

For example, let’s say we have a big file that contains a list of names, one per line. We can define a grammar for this file as follows:

vbnetCopy codegrammar NameList;

names: name+;

name: NAME;

NAME: [a-zA-Z]+;
WS: [ \t\n]+ -> skip;

This grammar defines a rule called names that matches one or more name rules. The name rule matches a string of one or more letters (upper or lower case). The WS rule matches any whitespace characters (spaces, tabs, newlines) and tells ANTLR4 to skip them.

With this grammar defined, we can generate a parser using the ANTLR4 tool. We can then use this parser to parse our big file:

scssCopy codefrom antlr4 import *
from NameListLexer import NameListLexer
from NameListParser import NameListParser

input_stream = FileStream("namelist.txt")
lexer = NameListLexer(input_stream)
stream = CommonTokenStream(lexer)
parser = NameListParser(stream)

tree = parser.names()

This code reads the contents of a file called “namelist.txt” and creates a parser object from it. It then calls the names rule of the parser, which returns a parse tree representing the structure of the file.

We can then use the parse tree to extract the data we need from the file. For example, we can extract all the names in the file like this:

scssCopy codeclass NameListListener(NameListParserListener):
    def enterName(self, ctx):
        print(ctx.getText())

listener = NameListListener()
walker = ParseTreeWalker()
walker.walk(listener, tree)

This code defines a listener object that prints out the text of any name rule that it encounters in the parse tree. It then creates a walker object and calls its walk() method to traverse the parse tree, passing in the listener object.

With this code, we can easily parse large files and extract the data we need from them using ANTLR4 in Python.

Parsing large files using ANTLR4 in Python

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