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# casrn.py - functions for handling CAS Registry Numbers
#
# Copyright (C) 2017 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
"""CAS RN (Chemical Abstracts Service Registry Number).
The CAS Registry Number is a unique identifier assigned by the Chemical
Abstracts Service (CAS) to a chemical substance.
More information:
* https://en.wikipedia.org/wiki/CAS_Registry_Number
>>> validate('87-86-5')
'87-86-5'
>>> validate('87-86-6')
Traceback (most recent call last):
...
InvalidChecksum: ...
"""
from stdnum.exceptions import *
from stdnum.util import clean
def compact(number):
"""Convert the number to the minimal representation."""
number = clean(number, ' ').strip()
if '-' not in number:
number = '-'.join((number[:-3], number[-3:-1], number[-1:]))
return number
def calc_check_digit(number):
"""Calculate the check digit for the number. The passed number should not
have the check digit included."""
number = number.replace('-', '')
return str(
sum((i + 1) * int(n) for i, n in enumerate(reversed(number))) % 10)
def validate(number):
"""Check if the number provided is a valid CAS RN."""
number = compact(number)
if not 7 <= len(number) <= 12:
raise InvalidLength()
if not number[:-5].isdigit() or not number[-4:-2].isdigit():
raise InvalidFormat()
if number[-2] != '-' or number[-5] != '-':
raise InvalidFormat()
if number[-1] != calc_check_digit(number[:-1]):
raise InvalidChecksum()
return number
def is_valid(number):
"""Check if the number provided is a valid CAS RN."""
try:
return bool(validate(number))
except ValidationError:
return False
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