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# vat.py - functions for handling Irish VAT numbers
#
# Copyright (C) 2012, 2013 Arthur de Jong
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301 USA
"""VAT (Irish VAT number).
The Irish VAT number consists of 8 digits. The last digit is a check
letter, the second digit may be a number, a letter, "+" or "*".
>>> validate('IE 6433435F')
'6433435F'
>>> validate('6433435E') # incorrect check digit
Traceback (most recent call last):
...
InvalidChecksum: ...
>>> validate('8D79739I') # old style number
'8D79739I'
>>> validate('8?79739J') # incorrect old style
Traceback (most recent call last):
...
InvalidFormat: ...
"""
from stdnum.exceptions import *
from stdnum.util import clean
def compact(number):
"""Convert the number to the minimal representation. This strips the
number of any valid separators and removes surrounding whitespace."""
number = clean(number, ' -').upper().strip()
if number.startswith('IE'):
number = number[2:]
return number
def calc_check_digit(number):
"""Calculate the check digit. The number passed should not have the
check digit included."""
alphabet = 'WABCDEFGHIJKLMNOPQRSTUV'
number = (7 - len(number)) * '0' + number
return alphabet[sum((8 - i) * int(n) for i, n in enumerate(number)) % 23]
def validate(number):
"""Checks to see if the number provided is a valid VAT number. This checks
the length, formatting and check digit."""
number = compact(number)
if not number[:1].isdigit() or not number[2:7].isdigit():
raise InvalidFormat()
if len(number) != 8:
raise InvalidLength()
if number[:7].isdigit():
# new system
if number[-1] != calc_check_digit(number[:-1]):
raise InvalidChecksum()
elif number[1] in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ+*':
# old system
if number[-1] != calc_check_digit(number[2:-1] + number[0]):
raise InvalidChecksum()
else:
raise InvalidFormat()
return number
def is_valid(number):
"""Checks to see if the number provided is a valid VAT number. This checks
the length, formatting and check digit."""
try:
return bool(validate(number))
except ValidationError:
return False
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