Fixed #5475 -- Added the Luhn check algorithm to django.utils.checksu…

…ms so that

localflavors don't have to reimplement it each time. Thanks, __hawkeye__.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6569 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/utils/checksums.py

@@ -0,0 +1,22 @@
+"""
+Common checksum routines (used in multiple localflavor/ cases, for example).
+"""
+
+__all__ = ['luhn',]
+
+LUHN_ODD_LOOKUP = (0, 2, 4, 6, 8, 1, 3, 5, 7, 9) # sum_of_digits(index * 2)
+
+def luhn(candidate):
+    """
+    Checks a candidate number for validity according to the Luhn
+    algorithm (used in validation of, for example, credit cards).
+    Both numeric and string candidates are accepted.
+    """
+    if not isinstance(candidate, basestring):
+        candidate = str(candidate)
+    try:
+        evens = sum([int(c) for c in candidate[-1::-2]])
+        odds = sum([LUHN_ODD_LOOKUP[int(c)] for c in candidate[-2::-2]])
+        return ((evens + odds) % 10 == 0)
+    except ValueError:  # Raised if an int conversion fails
+        return False

tests/regressiontests/utils/tests.py

@@ -4,7 +4,7 @@
 
 from unittest import TestCase
 
-from django.utils import html
+from django.utils import html, checksums
 
 from timesince import timesince_tests
 
@@ -116,6 +116,32 @@ def test_fix_ampersands(self):
         for value, output in items:
             self.check_output(f, value, output)
 
+class TestUtilsChecksums(TestCase):
+
+    def check_output(self, function, value, output=None):
+        """
+        Check that function(value) equals output.  If output is None,
+        check that function(value) equals value.
+        """
+        if output is None:
+            output = value
+        self.assertEqual(function(value), output)
+
+    def test_luhn(self):
+        f = checksums.luhn
+        items = (
+            (4111111111111111, True), ('4111111111111111', True),
+            (4222222222222, True), (378734493671000, True),
+            (5424000000000015, True), (5555555555554444, True),
+            (1008, True), ('0000001008', True), ('000000001008', True),
+            (4012888888881881, True), (1234567890123456789012345678909, True),
+            (4111111111211111, False), (42222222222224, False),
+            (100, False), ('100', False), ('0000100', False),
+            ('abc', False), (None, False), (object(), False),
+        )
+        for value, output in items:
+            self.check_output(f, value, output)
+
 __test__ = {
     'timesince_tests': timesince_tests,
 }