Do not rely on dicts.merge to change target
Also make dicts.merge actually not touch target. This is much cleaner
than modifying in place, especially since we assign the result of the
dicts.merge call to target most of the time anyway.
Patch by: Sverre Rabbelier
"""
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