Task: UPC







Python: 
import itertools
import re

RE_BARCODE = re.compile(
    r"^(?P<s_quiet> +)"  
    r"(?P<s_guard>
    r"(?P<left>[ 
    r"(?P<m_guard> 
    r"(?P<right>[ 
    r"(?P<e_guard>
    r"(?P<e_quiet> +)$"  
)

LEFT_DIGITS = {
    (0, 0, 0, 1, 1, 0, 1): 0,
    (0, 0, 1, 1, 0, 0, 1): 1,
    (0, 0, 1, 0, 0, 1, 1): 2,
    (0, 1, 1, 1, 1, 0, 1): 3,
    (0, 1, 0, 0, 0, 1, 1): 4,
    (0, 1, 1, 0, 0, 0, 1): 5,
    (0, 1, 0, 1, 1, 1, 1): 6,
    (0, 1, 1, 1, 0, 1, 1): 7,
    (0, 1, 1, 0, 1, 1, 1): 8,
    (0, 0, 0, 1, 0, 1, 1): 9,
}

RIGHT_DIGITS = {
    (1, 1, 1, 0, 0, 1, 0): 0,
    (1, 1, 0, 0, 1, 1, 0): 1,
    (1, 1, 0, 1, 1, 0, 0): 2,
    (1, 0, 0, 0, 0, 1, 0): 3,
    (1, 0, 1, 1, 1, 0, 0): 4,
    (1, 0, 0, 1, 1, 1, 0): 5,
    (1, 0, 1, 0, 0, 0, 0): 6,
    (1, 0, 0, 0, 1, 0, 0): 7,
    (1, 0, 0, 1, 0, 0, 0): 8,
    (1, 1, 1, 0, 1, 0, 0): 9,
}


MODULES = {
    " ": 0,
    "
}

DIGITS_PER_SIDE = 6
MODULES_PER_DIGIT = 7


class ParityError(Exception):
    


class ChecksumError(Exception):
    


def group(iterable, n):
    
    args = [iter(iterable)] * n
    return tuple(itertools.zip_longest(*args))


def parse(barcode):
    
    match = RE_BARCODE.match(barcode)

    
    
    left = group((MODULES[c] for c in match.group("left")), MODULES_PER_DIGIT)
    right = group((MODULES[c] for c in match.group("right")), MODULES_PER_DIGIT)

    
    left, right = check_parity(left, right)

    
    return tuple(
        itertools.chain(
            (LEFT_DIGITS[d] for d in left),
            (RIGHT_DIGITS[d] for d in right),
        )
    )


def check_parity(left, right):
    
    
    
    
    left_parity = sum(sum(d) % 2 for d in left)
    right_parity = sum(sum(d) % 2 for d in right)

    
    
    if left_parity == 0 and right_parity == DIGITS_PER_SIDE:
        _left = tuple(tuple(reversed(d)) for d in reversed(right))
        right = tuple(tuple(reversed(d)) for d in reversed(left))
        left = _left
    elif left_parity != DIGITS_PER_SIDE or right_parity != 0:
        
        error = tuple(
            itertools.chain(
                (LEFT_DIGITS.get(d, "_") for d in left),
                (RIGHT_DIGITS.get(d, "_") for d in right),
            )
        )
        raise ParityError(" ".join(str(d) for d in error))

    return left, right


def checksum(digits):
    
    odds = (digits[i] for i in range(0, 11, 2))
    evens = (digits[i] for i in range(1, 10, 2))

    check_digit = (sum(odds) * 3 + sum(evens)) % 10

    if check_digit != 0:
        check_digit = 10 - check_digit

    if digits[-1] != check_digit:
        raise ChecksumError(str(check_digit))

    return check_digit


def main():
    barcodes = [
        "         
        "        
        "         
        "       
        "         
        "          
        "         
        "        
        "         
        "        
        "        
    ]

    for barcode in barcodes:
        try:
            digits = parse(barcode)
        except ParityError as err:
            print(f"{err} parity error!")
            continue

        try:
            check_digit = checksum(digits)
        except ChecksumError as err:
            print(f"{' '.join(str(d) for d in digits)} checksum error! ({err})")
            continue

        print(f"{' '.join(str(d) for d in digits)}")


if __name__ == "__main__":
    main()