AoC day 3 part 2

data = open('input.txt').read().strip()
do = True
total = 0
for i in range(len(data)):
    chunk = data[i:]

    if chunk.startswith('do()'):
        do = True

    elif chunk.startswith("don't()"):
        do = False

    if not chunk.startswith('mul('):
        continue

    subchunk = chunk[4:] # 4 = "mul(" length
    try:

        pairs = subchunk.split(')', 1)[0].split(',')
        a = int(pairs[0])
        b = int(pairs[1])
        if do:
            total += a * b

    except:
        continue

print(total)