--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/app/django/utils/checksums.py Fri Jul 18 18:22:23 2008 +0000
@@ -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