87 lines
2.8 KiB
Python
87 lines
2.8 KiB
Python
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# sedol.py - functions for handling SEDOL numbers
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#
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# Copyright (C) 2015 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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"""SEDOL number (Stock Exchange Daily Official List number).
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The SEDOL number is a security identifier used in the United Kingdom and
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Ireland assigned by the London Stock Exchange. A SEDOL is seven characters
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in length consisting of six alphanumeric digits, followed by a check digit.
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>>> validate('B15KXQ8')
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'B15KXQ8'
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>>> validate('B15KXQ7')
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Traceback (most recent call last):
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...
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InvalidChecksum: ...
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>>> to_isin('B15KXQ8')
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'GB00B15KXQ89'
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"""
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from stdnum.exceptions import *
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from stdnum.util import clean
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# the letters allowed in an SEDOL (vowels are never used)
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_alphabet = '0123456789 BCD FGH JKLMN PQRST VWXYZ'
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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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return clean(number, ' ').strip().upper()
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def calc_check_digit(number):
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"""Calculate the check digits for the number."""
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weights = (1, 3, 1, 7, 3, 9)
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s = sum(w * _alphabet.index(n) for w, n in zip(weights, number))
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return str((10 - s) % 10)
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def validate(number):
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"""Checks to see if the number provided is valid. This checks the length
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and check digit."""
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number = compact(number)
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if not all(x in _alphabet for x in number):
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raise InvalidFormat()
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if len(number) != 7:
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raise InvalidLength()
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if number[0].isdigit() and not number.isdigit():
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# new style SEDOLs are supposed to start with a letter, old-style
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# numbers should be fully numeric
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raise InvalidFormat()
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if calc_check_digit(number[:-1]) != number[-1]:
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raise InvalidChecksum()
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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 valid. This checks the length
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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 to_isin(number):
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"""Convert the number to an ISIN."""
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from stdnum import isin
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return isin.from_natid('GB', number)
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