Advent of code, step 1: an unusual math context where operators have no priority!

dec18.py

#!/usr/bin/env python3

import itertools
from enum import Enum, auto
import re
import logging
import sys
import numbers

logging.basicConfig(level=logging.INFO, stream=sys.stderr)

logger = logging.getLogger('dec16')
logger.info("Log started")


def logexpr(*somestring, l=logging.DEBUG):
    if isinstance(l, str):
        l = getattr(logging, l)
    for arg in somestring:
        logger.log(l, f"{arg}\t=\t{repr(eval(arg))}")


def logexpr_info(somestring):
    logexpr(somestring, l=logging.INFO)

#logexpr=(lambda *w: [logger.debug("{}\t=\t{}".format(x,repr(eval(x)))) for x in w ])


fileName = 'input'
if (len(sys.argv) > 1):
    fileName = sys.argv[1]

logger.debug("Reading from file {fileName!r}")


def collect(stack):
    if len(stack) < 3:
        return
    if not callable(stack[-2]):
        return
    if not isinstance(stack[-1], numbers.Number):
        return
    if not isinstance(stack[-3], numbers.Number):
        return
    v2 = stack.pop()
    op = stack.pop()
    v1 = stack.pop()
    nv = op(v1, v2)
    stack.append(nv)


def rempar(stack):
    if len(stack) < 2:
        return
    if stack[-2] != '(':
        logger.error(f"Cannot close paren: {stack=}")
        raise Exception("Cannot close paren.")
    del stack[-2]


def parse(l):
    logger.debug(f'Parsing {l=}')
    stack = []

    while len(l) > 0:
        logger.debug(f'{stack=} {l=}')
        c = l[0]

        if c == ' ':
            pass
        elif c >= '0' and c <= '9':
            v = int(c)
            stack.append(v)
        elif c == '+':
            collect(stack)
            stack.append(lambda x, y: x + y)
        elif c == '-':
            collect(stack)
            stack.append(lambda x, y: x - y)
        elif c == '*':
            collect(stack)
            stack.append(lambda x, y: x * y)
        elif c == '(':
            stack.append(c)
        elif c == ')':
            collect(stack)
            rempar(stack)

        l = l[1:]

    collect(stack)
    if len(stack) != 1:
        logger.error(f"Stack not of size 1: {stack=}")
        raise Exception("Not a valid expression.")

    return stack.pop()


value = 0

with open(fileName) as f:
    for l in f:
        l = l.rstrip()
        number = parse(l)
        logger.debug(f'{l=} {number=}')
        value += number
    print(f"{value=}")