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# vat.py - functions for handling Irish VAT numbers
#
# Copyright (C) 2012 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 "*".
>>> compact('IE 6433435F')
'6433435F'
>>> is_valid('6433435F')
True
>>> is_valid('6433435E') # incorrect check digit
False
>>> is_valid('8D79739I') # old style number
True
>>> is_valid('8?79739J') # incorrect old style
False
"""
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 is_valid(number):
"""Checks to see if the number provided is a valid VAT number. This checks
the length, formatting and check digit."""
try:
number = compact(number)
except:
return False
if len(number) != 8 or not number[0].isdigit() or \
not number[2:7].isdigit():
return False
if number[:7].isdigit():
# new system
return number[-1] == calc_check_digit(number[:-1])
if number[1] in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ+*':
# old system
return number[-1] == calc_check_digit(number[2:-1] + number[0])
return False
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