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# rtn.py - functions for handling banking routing transit numbers
#
# Copyright (C) 2014 Lifealike Ltd
#
# 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
"""RTN (Routing transport number).
The routing transport number is a nine digit number used in the US banking
system for processing deposits between banks.
The last digit is a checksum.
>>> calc_check_digit('11100002')
'5'
>>> validate('111000025')
'111000025'
>>> validate('11100002') # Not nine digits
Traceback (most recent call last):
...
InvalidLength: ..
>>> validate('11100002B') # Not all numeric
Traceback (most recent call last):
...
InvalidFormat: ..
>>> validate('112000025') # bad checksum
Traceback (most recent call last):
...
InvalidChecksum: ..
"""
from stdnum.exceptions import *
from stdnum.util import clean, isdigits
def compact(number):
"""Convert the number to the minimal representation. This strips the
number of any surrounding whitespace."""
number = clean(number).strip()
return number
def calc_check_digit(number):
"""Calculate the check digit. The number passed should not have the
check digit included."""
digits = [int(c) for c in number]
checksum = (
7 * (digits[0] + digits[3] + digits[6]) +
3 * (digits[1] + digits[4] + digits[7]) +
9 * (digits[2] + digits[5])
) % 10
return str(checksum)
def validate(number):
"""Check if the number is a valid routing number. This checks the length
and check digit."""
number = compact(number)
if not isdigits(number):
raise InvalidFormat()
if len(number) != 9:
raise InvalidLength()
if calc_check_digit(number[:-1]) != number[-1]:
raise InvalidChecksum()
return number
def is_valid(number):
"""Check if the number is a valid RTN."""
try:
return bool(validate(number))
except ValidationError:
return False
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