Advent of code 2020, Day 18, Python3.9

day18.py

from sys import stdin
from operator import add, mul
from re import findall

def arg(cont, ts):
    res, ts = cont(ts[1:]) if ts[0] == '(' else (int(ts[0]), ts)
    return res, ts[1:]

def parse(ops, term, cont, ts):
    lh, ts = term(cont, ts)
    while ts and (ts[0] in ops):
        op, ts = (add if ts[0] == '+' else mul, ts[1:])
        rh, ts = term(cont, ts)
        lh = op(lh, rh)
    return lh, ts

def part1(ts):
    return parse("+*", arg, part1, ts)

def part2(ts):
    def part2inner(cont, ts):
        return parse("+", arg, cont, ts)
    return parse("*", part2inner, part2, ts)

tokens = [findall('\(|\)|\*|\+|\d+', l) for l in stdin]
solve = lambda part: sum(v for v, _ in (part(ts) for ts in tokens))
print(solve(part1), solve(part2))