1 files changed, 28 insertions, 9 deletions
diff --git a/stdnum/luhn.py b/stdnum/luhn.py
index dbfb183..bc1b5ac 100644
--- a/stdnum/luhn.py
+++ b/stdnum/luhn.py
@@ -1,6 +1,6 @@
 # luhn.py - functions for performing the Luhn and Luhn mod N algorithms
 #
-# Copyright (C) 2010, 2011, 2012 Arthur de Jong
+# Copyright (C) 2010, 2011, 2012, 2013 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
@@ -22,24 +22,30 @@
 The Luhn algorithm is used to detect most accidental errors in various
 identification numbers.
 
->>> is_valid('7894')
-False
+>>> validate('7894')
+Traceback (most recent call last):
+    ...
+InvalidChecksum: ...
 >>> checksum('7894')
 6
 >>> calc_check_digit('7894')
 '9'
->>> is_valid('78949')
-True
+>>> validate('78949')
+'78949'
 
 An alternative alphabet can be provided to use the Luhn mod N algorithm.
 The default alphabet is '0123456789'.
 
->>> is_valid('1234', alphabet='0123456789abcdef')
-False
+>>> validate('1234', alphabet='0123456789abcdef')
+Traceback (most recent call last):
+    ...
+InvalidChecksum: ...
 >>> checksum('1234', alphabet='0123456789abcdef')
 14
 """
 
+from stdnum.exceptions import *
+
 
 def checksum(number, alphabet='0123456789'):
     """Calculate the Luhn checksum over the provided number. The checksum
@@ -52,11 +58,24 @@ def checksum(number, alphabet='0123456789'):
                 for i in number[1::2])) % n
 
 
-def is_valid(number, alphabet='0123456789'):
+def validate(number, alphabet='0123456789'):
     """Checks to see if the number provided passes the Luhn checksum."""
+    if not bool(number):
+        raise InvalidFormat()
     try:
-        return bool(number) and checksum(number, alphabet) == 0
+        valid = checksum(number, alphabet) == 0
     except:
+        raise InvalidFormat()
+    if not valid:
+        raise InvalidChecksum()
+    return number
+
+
+def is_valid(number, alphabet='0123456789'):
+    """Checks to see if the number provided passes the Luhn checksum."""
+    try:
+        return bool(validate(number, alphabet))
+    except ValidationError:
         return False