Arthur de Jong

Open Source / Free Software developer

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# vat.py - functions for handling Swedish VAT numbers
# coding: utf-8
#
# 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

"""Module for handling Swedish VAT (Moms, Mervärdesskatt) numbers.

The Momsregistreringsnummer consists of 12 digits of which the last two
should be 01. The first 10 digits should have a valid Luhn checksum.

>>> compact('SE 123456789701')
'123456789701'
>>> is_valid('123456789701')
True
>>> is_valid('123456789101')  # invalid check digits
False
"""

from stdnum import luhn
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('SE'):
        number = number[2:]
    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:
        number = compact(number)
    except:
        return False
    return number.isdigit() and len(number) == 12 and \
           luhn.is_valid(number[:-2]) and 0 < int(number[-2:]) < 95