+
−"""
+
−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