1 files changed, 22 insertions, 0 deletions
diff --git a/webapp/django/utils/checksums.py b/webapp/django/utils/checksums.py
new file mode 100644
index 0000000000..970f563f38
--- /dev/null
+++ b/webapp/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