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# cvr.py - functions for handling Danish CVR 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
"""CVR (Momsregistreringsnummer, Danish VAT number).
The CVR (Momsregistreringsnummer, VAT) is an 8 digit number with a
straightforward check mechanism.
>>> compact('DK 13585628')
'13585628'
>>> is_valid('DK 13585628')
True
>>> is_valid('DK 13585627')
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('DK'):
number = number[2:]
return number
def checksum(number):
"""Calculate the checksum."""
weights = (2, 7, 6, 5, 4, 3, 2, 1)
return sum(weights[i] * int(n) for i, n in enumerate(number)) % 11
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 len(number) == 8 and number.isdigit() and \
number[0] != '0' and checksum(number) == 0
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