ANTLR4 extraneous input - antlr4

Question

I have a problem with my ANTLR4. I'm trying to print AST from python 3 code but there are some errors and I don't know how to fix them.
I wrote simple code for test:
a=(1,2,3)
print(a)
I ran the program but this errors appeared:
line 1:1 extraneous input '=' expecting {<EOF>, '.', '*', '(', '**', '[', '|', '^', '&', '<<', '>>', '+', '-', '/', '%', '//', '#'}
line 2:0 extraneous input '\n' expecting {<EOF>, '.', '*', '(', '**', '[', '|', '^', '&', '<<', '>>', '+', '-', '/', '%', '//', '#'}
line 3:0 extraneous input '\n' expecting {<EOF>, '.', '*', '(', '**', '[', '|', '^', '&', '<<', '>>', '+', '-', '/', '%', '//', '#'}
My main class :
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
import org.antlr.v4.*;
public class Main {
public static void main(String[] args) {
try {
ANTLRInputStream input = new ANTLRFileStream("/home/grzegorz/Desktop/Python3/input.txt");
Python3Lexer lexer = new Python3Lexer(input);
CommonTokenStream token = new CommonTokenStream(lexer);
Python3Parser parser = new Python3Parser(token);
ParseTree parseTree = parser.expr();
System.out.println(parseTree.toStringTree(parser));
}catch (Exception ex){
ex.printStackTrace();
}
}
}
I have the grammar from this site:
https://github.com/antlr/grammars-v4/tree/master/python3

Answer 1

Explanation
Your input file consists of two statements and you are parsing the file as if it was an expression (with line ParseTree parseTree = parser.expr();; rule expr from Python 3 grammar).
This also exaplains the first error: an identificator a is accepted as a part of expression but = sign is not. That's because = is a part of assignment statement.
Solution
Parse the input using another grammar rule for example file_input rule which will accept many statements. Change the abovementioned line to ParseTree parseTree = parser.file_input();.