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# pvn.py - functions for handling Latvian PVN (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 Latvian PVN (Pievienotās vērtības nodokļa, VAT)
numbers.
It is a 11 digit number that can either be a reference to a legal entity
(in which case the first digit > 3) or a natural person (in which case it
should be the same as the personal code (personas kods)). Personal codes
start with 6 digits to denote the birth date in the form ddmmyy.
>>> compact('LV 4000 3521 600')
'40003521600'
>>> is_valid('40003521600')
True
>>> is_valid('40003521601') # invalid check digit
False
>>> is_valid('161175-19997') # personal code
True
>>> is_valid('161375-19997') # invalid date
False
"""
import datetime
from stdnum.util import clean
# validation functions are available on-line but it is not allowed
# to perform automated queries:
# http://www6.vid.gov.lv/VID_PDB?aspxerrorpath=/vid_pdb/pvn.asp
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('LV'):
number = number[2:]
return number
def checksum(number):
"""Calculate the checksum for legal entities."""
weights = (9, 1, 4, 8, 3, 10, 2, 5, 7, 6, 1)
return sum(weights[i] * int(n) for i, n in enumerate(number)) % 11
def calc_check_digit_pers(number):
"""Calculate the check digit for personal codes. The number passed
should not have the check digit included."""
# note that this algorithm has not been confirmed by an independent source
weights = (10, 5, 8, 4, 2, 1, 6, 3, 7, 9)
check = 1 + sum(weights[i] * int(n) for i, n in enumerate(number))
return str(check % 11 % 10)
def get_birth_date(number):
"""Split the date parts from the number and return the birth date."""
day = int(number[0:2])
month = int(number[2:4])
year = int(number[4:6])
year += 1800 + int(number[6]) * 100
return datetime.date(year, month, day)
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) != 11 or not number.isdigit():
return False
if number[0] > '3':
# legal entity
return checksum(number) == 3
else:
# natural resident, check if birth date is valid
try:
birth_date = get_birth_date(number)
# TODO: check that the birth date is not in the future
except ValueError, e:
return False
return calc_check_digit_pers(number[:-1]) == number[-1]
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