ANTLR 4 Python 3 Runtime

import os
from antlr4 import InputStream, CommonTokenStream, ParseTreeWalker

# --- BEGIN: Dummy generated classes for demonstration ---
# In a real scenario, these would be generated by the ANTLR tool:
# java -jar antlr-4.x.x-complete.jar -Dlanguage=Python3 MyGrammar.g4

class MyGrammarLexer:
    def __init__(self, input_stream): pass
    def getAllTokens(self): return []

class MyGrammarParser:
    def __init__(self, token_stream): pass
    def startRule(self): return None # Replace 'startRule' with your grammar's entry rule

class MyGrammarListener:
    def enterEveryRule(self, ctx): pass
    def exitEveryRule(self, ctx): pass
    # ... other enter/exit methods for your grammar rules

# --- END: Dummy generated classes ---

# Assuming MyGrammar.g4 contains:
# grammar MyGrammar;
# startRule: 'hello' ID EOF;
# ID: [a-zA-Z]+;
# WS: [ \t\r\n]+ -> skip;

def parse_input(text):
    input_stream = InputStream(text)
    lexer = MyGrammarLexer(input_stream) # Use your generated Lexer class
    stream = CommonTokenStream(lexer)
    parser = MyGrammarParser(stream)    # Use your generated Parser class
    
    # Optionally, set up error handling
    # parser.removeErrorListeners()
    # parser.addErrorListener(MyCustomErrorListener())
    
    tree = parser.startRule() # Call the entry rule of your grammar
    
    # Optionally, walk the parse tree with a listener or visitor
    # walker = ParseTreeWalker()
    # listener = MyGrammarListener() # Use your generated Listener/Visitor class
    # walker.walk(listener, tree)
    
    print(f"Parse tree: {tree.toStringTree(recog=parser)}")

if __name__ == '__main__':
    # Simulate user input or a file content
    # For a real application, you might read from stdin or a file
    test_input = os.environ.get('ANTLR_TEST_INPUT', 'hello world')
    print(f"Parsing: '{test_input}'")
    parse_input(test_input)
    print("Note: In a real scenario, 'MyGrammarLexer' and 'MyGrammarParser' would be generated .py files from your .g4 grammar using the ANTLR Java tool.")