day11.py

#!/usr/bin/env python3

import re
from math import gcd
from copy import deepcopy
from collections import deque
from operator import add, mul, attrgetter

import sys

class Monkey:
	__slots__ = (
		'items', 'op', 'op_value', 'divisor',
		'pass_if_true', 'pass_if_false', 'inspections'
	)

	def inspect(self):
		item = self.items.popleft()
		if self.op_value is None:
			return self.op(item, item)
		return self.op(item, self.op_value)

# math.lcm() is Python 3.9+
def lcm(*integers):
	it  = iter(integers)
	res = next(it)

	for x in it:
		res = res * x // gcd(res, x)
	return res

def simulate(monkeys, n_rounds, part2=False):
	if part2:
		modulus = lcm(*map(attrgetter('divisor'), monkeys))

	for _ in range(n_rounds):
		for m in monkeys:
			m.inspections += len(m.items)

			while m.items:
				if part2:
					item = m.inspect() % modulus
				else:
					item = m.inspect() // 3

				if item % m.divisor == 0:
					monkeys[m.pass_if_true].items.append(item)
				else:
					monkeys[m.pass_if_false].items.append(item)

	a, b = sorted(map(attrgetter('inspections'), monkeys), reverse=True)[:2]
	return a * b


# Open the first argument as input or use stdin if no arguments were given
fin = open(sys.argv[1]) if len(sys.argv) > 1 else sys.stdin

regexp      = re.compile(r'\d+')
raw_monkeys = fin.read().split('\n\n')
monkeys     = []

for raw_monkey in raw_monkeys:
	lines   = raw_monkey.splitlines()
	matches = regexp.findall(lines[2])

	m = Monkey()
	m.items         = deque(map(int, regexp.findall(lines[1])))
	m.op            = add if '+' in lines[2] else mul
	m.op_value      = int(matches[0]) if matches else None
	m.divisor       = int(regexp.findall(lines[3])[0])
	m.pass_if_true  = int(regexp.findall(lines[4])[0])
	m.pass_if_false = int(regexp.findall(lines[5])[0])
	m.inspections   = 0
	monkeys.append(m)

original = deepcopy(monkeys)

answer1 = simulate(monkeys, 20)
print('Part 1:', answer1)

answer2 = simulate(original, 10000, True)
print('Part 2:', answer2)