Return check digits in 02-98 range for ISO 7064 Mod 97, 10

arthurdejong · arthurdejong · commit e2a27743b3f8 · 2022-03-21T14:20:27.000+01:00
There are some valid ranges for check digits within ISO 7064 Mod 97, 10 that all result in a valid checksum. This changes the calculated check digits to be in the range from 02 to 98 as is specified for use in IBAN. See https://en.wikipedia.org/wiki/International_Bank_Account_Number#Generating_IBAN_check_digits Closes arthurdejong#289
diff --git a/stdnum/iso7064/mod_97_10.py b/stdnum/iso7064/mod_97_10.py
@@ -1,6 +1,6 @@
 # mod_97_10.py - functions for performing the ISO 7064 Mod 97, 10 algorithm
 #
-# Copyright (C) 2010-2021 Arthur de Jong
+# Copyright (C) 2010-2022 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
@@ -51,7 +51,7 @@ def checksum(number):
 def calc_check_digits(number):
     """Calculate the extra digits that should be appended to the number to
     make it a valid number."""
-    return '%02d' % ((98 - 100 * checksum(number)) % 97)
+    return '%02d' % (98 - checksum(number + '00'))
 
 
 def validate(number):
diff --git a/tests/test_iso7064.doctest b/tests/test_iso7064.doctest
@@ -1,6 +1,6 @@
 test_doctest - more detailed doctests for the stdnum.iso7064 package
 
-Copyright (C) 2010, 2011, 2013 Arthur de Jong
+Copyright (C) 2010-2022 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
@@ -68,3 +68,14 @@ These normal tests of Mod 37, 2 should just work
 
 >>> mod_37_2.calc_check_digit('G123498654321')
 'H'
+
+
+The Mod 97, 10 check digit suggestion should prefer check digits in the
+range of 02 to 98 as is used in IBAN.
+
+>>> mod_97_10.calc_check_digits('5367')
+'02'
+>>> mod_97_10.calc_check_digits('5303')
+'97'
+>>> mod_97_10.calc_check_digits('5335')
+'98'

Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	`# mod_97_10.py - functions for performing the ISO 7064 Mod 97, 10 algorithm`
`2`	`2`	`#`
`3`		`-# Copyright (C) 2010-2021 Arthur de Jong`
	`3`	`+# Copyright (C) 2010-2022 Arthur de Jong`
`4`	`4`	`#`
`5`	`5`	`# This library is free software; you can redistribute it and/or`
`6`	`6`	`# modify it under the terms of the GNU Lesser General Public`
`@@ -51,7 +51,7 @@ def checksum(number):`
`51`	`51`	`def calc_check_digits(number):`
`52`	`52`	`"""Calculate the extra digits that should be appended to the number to`
`53`	`53`	`make it a valid number."""`
`54`		`- return '%02d' % ((98 - 100 * checksum(number)) % 97)`
	`54`	`+ return '%02d' % (98 - checksum(number + '00'))`
`55`	`55`
`56`	`56`
`57`	`57`	`def validate(number):`