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"""

https://en.wikipedia.org/wiki/Check_digit#Algorithms

"""

def get_check_digit(barcode: int) -> int:

"""

Returns the last digit of barcode by excluding the last digit first

and then computing to reach the actual last digit from the remaining

12 digits.

>>> get_check_digit(8718452538119)

>>> get_check_digit(87184523)

>>> get_check_digit(87193425381086)

>>> [get_check_digit(x) for x in range(0, 100, 10)]

[0, 7, 4, 1, 8, 5, 2, 9, 6, 3]

"""

barcode //= 10 # exclude the last digit

checker = False

s = 0

# extract and check each digit

while barcode != 0:

mult = 1 if checker else 3

s += mult * (barcode % 10)

barcode //= 10

checker = not checker

return (10 - (s % 10)) % 10

def is_valid(barcode: int) -> bool:

"""

Checks for length of barcode and last-digit

Returns boolean value of validity of barcode

>>> is_valid(8718452538119)

True

>>> is_valid(87184525)

False

>>> is_valid(87193425381089)

False

>>> is_valid(0)

False

>>> is_valid(dwefgiweuf)

Traceback (most recent call last):

...

NameError: name 'dwefgiweuf' is not defined

"""

return len(str(barcode)) == 13 and get_check_digit(barcode) == barcode % 10

def get_barcode(barcode: str) -> int:

"""

Returns the barcode as an integer

>>> get_barcode("8718452538119")

8718452538119

>>> get_barcode("dwefgiweuf")

Traceback (most recent call last):

...

ValueError: Barcode 'dwefgiweuf' has alphabetic characters.

"""

if str(barcode).isalpha():

msg = f"Barcode '{barcode}' has alphabetic characters."

raise ValueError(msg)

elif int(barcode) < 0:

raise ValueError("The entered barcode has a negative value. Try again.")

else:

return int(barcode)

if __name__ == "__main__":

import doctest

doctest.testmod()

"""

Enter a barcode.

"""

barcode = get_barcode(input("Barcode: ").strip())

if is_valid(barcode):

print(f"'{barcode}' is a valid barcode.")

else:

print(f"'{barcode}' is NOT a valid barcode.")

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