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# vat.py - functions for handling Finnish VAT numbers
# coding: utf-8
#
# 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
"""ALV nro (Arvonlisäveronumero, Finnish VAT number).
The number is an 8-digit code with a weighted checksum.
>>> validate('FI 20774740')
'20774740'
>>> validate('FI 20774741') # invalid check digit
Traceback (most recent call last):
...
InvalidChecksum: ...
"""
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('FI'):
number = number[2:]
return number
def checksum(number):
"""Calculate the checksum."""
weights = (7, 9, 10, 5, 8, 4, 2, 1)
return sum(weights[i] * int(n) for i, n in enumerate(number)) % 11
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.isdigit():
raise InvalidFormat()
if len(number) != 8:
raise InvalidLength()
if checksum(number) != 0:
raise InvalidChecksum()
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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