day3.py

def read_num(line, j):
    num = ""
    while line[j] in "0123456789":
        num += line[j]
        j += 1
    return j, int(num)
def check(line, j, s):
    return line[j:j+len(s)] == s

file = open("day3.csv", "r")
sum = 0
for line in file.read().splitlines():
    enabled = True
    for i in range(len(line)):
        j = i
        if enabled:
            if check(line, j, "mul("):
                j += 4
                if line[j] in "0123456789":
                    j, num1 = read_num(line, j)
                    if check(line, j, ','):
                        j += 1
                        j, num2 = read_num(line, j)
                        if check(line, j, ')'):
                            j += 1
                            sum += num1 * num2
            elif check(line, j, "don't()"):
                j += 7
                enabled = False
        elif check(line, j, "do()"):
            j += 4
            enabled = True
print(sum)