lisp_parser.py

import re


def _parse_sequence(sequence):
    remainder_to_parse = sequence
    tokens = []
    while len(remainder_to_parse) > 0:
        match2 = re.match(r"^(\(.*\))", remainder_to_parse)
        if match2 is not None:
            token = match2.group(1)
        else:
            token = remainder_to_parse.split()[0]
        tokens.append(token)
        remainder_to_parse = remainder_to_parse[len(token) + 1 :]
    return [parse(token) for token in tokens]


def parse(input_text):
    match = re.match(r"^\((.*)\)$", input_text)
    if match is not None:
        return _parse_sequence(match.group(1))

    if input_text.isdigit():
        return int(input_text)
    return input_text


if __name__ == "__main__":
    print(parse(input()))

lisp_parser_test.py

import unittest
from lisp_parser import parse


class TestLispParser(unittest.TestCase):
    def test_parse_single_digit(self):
        self.assertEqual(parse("(1)"), [1])

    def test_parse_addition(self):
        self.assertEqual(parse("(+ 1 2)"), ["+", 1, 2])

    def test_parse_nested_expression(self):
        self.assertEqual(parse("(list (+ 1 2) 9)"), ["list", ["+", 1, 2], 9])

    def test_parse_example(self):
        self.assertEqual(
            parse("(first (list 1 (+ 2 3) 9))"), ["first", ["list", 1, ["+", 2, 3], 9]]
        )