74 lines
2.4 KiB
Python
74 lines
2.4 KiB
Python
# utr.py - functions for handling English UTRs
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#
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# Copyright (C) 2020 Holvi Payment Services
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# Copyright (C) 2020 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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"""UTR (United Kingdom Unique Taxpayer Reference).
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A UTR (unique taxpayer reference) is a 10 digit number used to identify UK
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taxpayers who have to submit a tax return.
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More information:
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* https://www.oecd.org/tax/automatic-exchange/crs-implementation-and-assistance/tax-identification-numbers/UK-TIN.pdf
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>>> validate('1955839661')
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'1955839661'
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>>> validate('2955839661')
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Traceback (most recent call last):
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...
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InvalidChecksum: ..
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"""
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from __future__ import annotations
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from stdnum.exceptions import *
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from stdnum.util import clean, isdigits
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def compact(number: str) -> str:
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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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return clean(number, ' ').upper().strip().lstrip('K')
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def calc_check_digit(number: str) -> str:
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"""Calculate the check digit for the number. The passed number should not
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have the check digit (the first one) included."""
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weights = (6, 7, 8, 9, 10, 5, 4, 3, 2)
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return '21987654321'[sum(int(n) * w for n, w in zip(number, weights)) % 11]
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def validate(number: str) -> str:
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"""Check if the number is a valid UTR."""
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number = compact(number)
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if not isdigits(number):
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raise InvalidFormat()
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if not len(number) == 10:
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raise InvalidLength()
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if number[0] != calc_check_digit(number[1:]):
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raise InvalidChecksum()
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return number
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def is_valid(number: str) -> bool:
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"""Check if the number is a valid UTR."""
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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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