Answer by blacktide for How to safely verify a file contains valid Python syntax in java?

I believe the issue is with the Python 3.12 grammar in the grammars-v4 repository. I used your code as a base, and was able to get it working properly using the grammars in the ANTLR4-parser-for-Python-3.12 repository.

Here's the full working code:

package playground;import org.antlr.v4.runtime.CharStream;import org.antlr.v4.runtime.CharStreams;import org.antlr.v4.runtime.CommonTokenStream;import playground.antlr.generated.PythonLexer;import playground.antlr.generated.PythonParser;import java.io.ByteArrayOutputStream;import java.io.PrintStream;import java.util.List;public class PythonValidator {    public static void main(String[] args) {        List<String> snippets = List.of(            // Hello world as a function"""            def foo():                print("hello world.")            foo()""",            // Program to generate a random number between 0 and 0"""            # Program to generate a random number between 0 and 9            import random            print(random.randint(0,9))""",            // Reverse a number"""            num = 1234            reversed_num = 0            while num != 0:                digit = num % 10                reversed_num = reversed_num * 10 + digit                num //= 10            print("Reversed Number: " + str(reversed_num))    """        );        PythonValidator validator = new PythonValidator();        for (String snippet : snippets) {            boolean valid = validator.isValidSyntax(snippet);            System.out.println("Valid? " + valid);        }    }    public boolean isValidSyntax(String pythonCode) {        PythonParser parser = getPythonParser(pythonCode);        // Redirect standard error stream        PrintStream originalErr = System.err;        ByteArrayOutputStream errStream = new ByteArrayOutputStream();        System.setErr(new PrintStream(errStream));        try {            parser.file_input();        } finally {            // Restore the original standard error stream            System.setErr(originalErr);        }        // Check if there were any errors in the error stream        String errorOutput = errStream.toString();        if (!errorOutput.isEmpty()) {            System.out.println(errorOutput);            return false;        } else {            return true;        }    }    private PythonParser getPythonParser(String pythonCode) {        // Create a CharStream from the Python code        CharStream charStream = CharStreams.fromString(pythonCode);        // Create the lexer        PythonLexer lexer = new PythonLexer(charStream);        // Create a token stream from the lexer        CommonTokenStream tokenStream = new CommonTokenStream(lexer);        // Create the parser        return new PythonParser(tokenStream);    }}

Here is a working example.

Just clone the repo and run:

./gradlew generateGrammarSource./gradlew run