Advent of code 2023 day 4

def day4(s, *, part2=False):
  copies = collections.Counter()
  total = 0

  for card_id, line in enumerate(s.splitlines()):
    winning, have = map(str.split, line.split(':')[1].split(' | '))
    num_matches = len(set(winning) & set(have))
    if part2:
      value = 1 + copies[card_id]
      for i in range(num_matches):
        copies[card_id + 1 + i] += value
      total += value
    elif num_matches:
      total += 2 ** (num_matches - 1)

  return total