solution.py

def is_valid_barcode(value):
    if not isinstance(value, str):
        return False

    if len(value) not in [8, 12, 13, 14, 17, 18]:
        return False
    if len(value) != 18:
        number_zero_to_add = 18 - len(value)
        value = '0' * number_zero_to_add + value

    try:
        value = int(value)
    except :
        return False

    value = str(value)

    sum = 0
    digit = int(value[-1])
    value = value[:-1:]
    for interger in value[::2]:
        sum += int(interger) * 3
    for interger in value[1::2]:
        sum += int(interger)
    if check_degit(sum) == digit:
        return True

    return False


def check_degit(value):
    result = (value % 10)
    if result > 0:
        result = 10 - result
    return result

test.py

# encoding: utf-8

# The goal of the exercise is to write the function is_valid_barcode which:
#   - returns True if the given parameter is:
#       - a string
#       - which is a valid GTIN, GSIN or SSCC (see https://www.gs1.org/services/how-calculate-check-digit-manually)
#   - returns False in EVERY other case
# This function should never raise an exception
#
# Precisions on the barcode format:
#   - GTINs are made of 8, 12, 13 or 14 digits, GSIN are 17 characters and SSCC are 18 characters long.
#   - the last one is a check digit, i.e. it can be calculated from the others
#   - if the calculated check digit differs from the actual check digit, then the string is considered as an invalid GTIN


def is_valid_barcode(value):
    return False


test_cases = [
    ('6291041500213', True), # <--- example of the spec
    ('6291041500211', False), # <-- example with wrong check digit
    ('3124482010481', True),
    ('3124482010482', False),
    ('3124482010483', False),
    ('3124482010484', False),
    ('3124482010485', False),
    ('3124482010486', False),
    ('3124482010487', False),
    ('3124482010488', False),
    ('3124482010489', False),
    ('3124482010480', False),
    ('0167053164698', True),
    ('13033490913240', True),
    ('13033490913240.00', False),
    ('123456017450', True),
    ('12345670', True),
    ('000000000000000000000', False),
    ('00000000000000000000', False),
    ('0000000000000000000', False),
    ('000000000000000000', True),
    ('00000000000000000', True),
    ('0000000000000000', False),
    ('000000000000000', False),
    ('00000000000000', True),
    ('0000000000000', True),
    ('000000000000', True),
    ('00000000000', False),
    ('0000000000', False),
    ('000000000', False),
    ('00000000', True),
    ('0000000', False),
    ('000000', False),
    ('00000', False),
    ('0000', False),
    ('000', False),
    ('00', False),
    ('0', False),
    ('zerozerozerozero', False),
    ("I am not a GTIN!4", False),
    ('0000OOOO000000000', False),
    ('ßþéçíæL ĉĥâ®åCẗëR§ ΅œ’', False),
    ([0,0,0,0,0,0,0,0], False),
    (3124482010481, False),
]

for test, expected in test_cases:
    try:
        result = is_valid_barcode(test)
    except Exception as e:
        print("Failed: %s -> %s" % (test, e))
        raise
    if result != expected:
        print("Failed: %s -> expected %s got %s" % (test, expected, result))
        break
else:
    print("Success")