Advent of code 2023 day 15

def day15(s, *, part2=False):
  s = s.strip()

  def my_hash(s2):
    # return 0 if not s2 else ((my_hash(s2[:-1]) + ord(s2[-1])) * 17) % 256
    h = 0
    for ch in s2:
      h = ((h + ord(ch)) * 17) % 256
    return h

  if not part2:
    return sum(my_hash(instruction) for instruction in s.split(','))

  boxes = [[] for _ in range(256)]
  for instruction in s.split(','):
    label, op, focal = hh.re_groups(r'^(.+)([-=])(.*)$', instruction)
    box_index = my_hash(label)
    if op == '-':
      boxes[box_index] = [(l, f) for l, f in boxes[box_index] if l != label]
    else:
      indices = [i for i, (l, f) in enumerate(boxes[box_index]) if l == label]
      if indices:
        boxes[box_index][indices[0]] = label, focal
      else:
        boxes[box_index].append((label, focal))

  return sum((b + 1) * (i + 1) * int(f) for b in range(256) for i, (l, f) in enumerate(boxes[b]))