UPC / EAN

[Jochen Garcke <jochen [at] garcke.de>]

Maybe of interest, feel free to use the code.

I needed to validate barcodes of the form UPC or EAN-13, with potential
additional EAN-2 or EAN-5 for periodicals, this code validates it.

Not sure if for a general code one would/should do the checks to remove
EAN5 and EAN2 though, one might get into trouble doing this always.

A separation into is_valid and calc_check_digit is obvious.

Jochen

def valid_barcode(barcode):
    '''
    validates a barcode
    - ignore the check digit
    - count from right to left
    - add odd numbered times 3
    - add even numbered
    - 10 - (result modulo 10) is check digit
    - check digit of 10 becomes 0
    '''

    # remove space and hyphens
    barcode = str(barcode).replace('-', '').replace(' ', '')
    try:
        int(barcode)
    except ValueError:
        return False

    # if extra 5 digits remove them (EAN 5)
    if len(barcode) > 16:
        barcode = barcode[:-5]
    elif len(barcode) > 13:
        # if extra 2 digits remove them (EAN 2)
        barcode = barcode[:-2]

    if len(barcode) > 13:
        return False

    odd = True
    check_sum = 0
    # odd/even from back
    for number in barcode[:-1][::-1]:
        if odd:
            check_sum += int(number)*3
        else:
            check_sum += int(number)
        odd = not odd

    check_digit = 10 - (check_sum % 10)
    if check_digit == 10:
        check_digit = 0
    if int(barcode[-1]) == check_digit:
        return True
    else:
        return False
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