122 lines
4.2 KiB
Python
122 lines
4.2 KiB
Python
# vat.py - functions for handling United Kingdom VAT numbers
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#
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# Copyright (C) 2012, 2013 Arthur de Jong
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301 USA
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"""VAT (United Kingdom (and Isle of Man) VAT registration number).
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The VAT number can either be a 9-digit standard number, a 12-digit standard
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number followed by a 3-digit branch identifier, a 5-digit number for
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government departments (first two digits are GD) or a 5-digit number for
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health authorities (first two digits are HA). The 9-digit variants use a
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weighted checksum.
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>>> validate('GB 980 7806 84')
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'980780684'
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>>> validate('802311781') # invalid check digit
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Traceback (most recent call last):
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...
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InvalidChecksum: ...
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>>> format('980780684')
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'980 7806 84'
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"""
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from stdnum.util import clean
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from stdnum.exceptions import *
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def compact(number):
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"""Convert the number to the minimal representation. This strips the
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number of any valid separators and removes surrounding whitespace."""
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number = clean(number, ' -.').upper().strip()
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if number.startswith('GB'):
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number = number[2:]
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return number
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def checksum(number):
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"""Calculate the checksum. The checksum is only used for the 9 digits
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of the number and the result can either be 0 or 42."""
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weights = (8, 7, 6, 5, 4, 3, 2, 10, 1)
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return sum(weights[i] * int(n) for i, n in enumerate(number)) % 97
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def validate(number):
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"""Checks to see if the number provided is a valid VAT number. This
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checks the length, formatting and check digit."""
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number = compact(number)
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if len(number) == 5:
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if not number[2:].isdigit():
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raise InvalidFormat()
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if number.startswith('GD') and int(number[2:]) < 500:
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# government department
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pass
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elif number.startswith('HA') and int(number[2:]) >= 500:
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# health authority
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pass
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else:
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raise InvalidComponent()
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elif len(number) == 11 and number[0:6] in ('GD8888', 'HA8888'):
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if not number[6:].isdigit():
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raise InvalidFormat()
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if number.startswith('GD') and int(number[6:9]) < 500:
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# government department
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pass
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elif number.startswith('HA') and int(number[6:9]) >= 500:
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# health authority
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pass
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else:
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raise InvalidComponent()
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if int(number[6:9]) % 97 != int(number[9:11]):
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raise InvalidChecksum()
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elif len(number) in (9, 12):
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if not number.isdigit():
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raise InvalidFormat()
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# standard number: nnn nnnn nn
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# branch trader: nnn nnnn nn nnn (ignore the last thee digits)
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# restarting: 100 nnnn nn
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if int(number[:3]) >= 100:
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if checksum(number[:9]) not in (0, 42, 55):
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raise InvalidChecksum()
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else:
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if checksum(number[:9]) != 0:
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raise InvalidChecksum()
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else:
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raise InvalidLength()
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return number
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def is_valid(number):
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"""Checks to see if the number provided is a valid VAT number. This
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checks the length, formatting and check digit."""
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try:
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return bool(validate(number))
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except ValidationError:
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return False
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def format(number):
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"""Reformat the passed number to the standard format."""
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number = compact(number)
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if len(number) == 5:
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# government department or health authority
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return number
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if len(number) == 12:
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# includes branch number
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return number[:3] + ' ' + number[3:7] + ' ' + number[7:9] + ' ' + number[9:]
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# standard number: nnn nnnn nn
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return number[:3] + ' ' + number[3:7] + ' ' + number[7:]
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