23 lines
748 B
Python
23 lines
748 B
Python
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"""
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Common checksum routines (used in multiple localflavor/ cases, for example).
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"""
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__all__ = ['luhn',]
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LUHN_ODD_LOOKUP = (0, 2, 4, 6, 8, 1, 3, 5, 7, 9) # sum_of_digits(index * 2)
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def luhn(candidate):
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"""
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Checks a candidate number for validity according to the Luhn
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algorithm (used in validation of, for example, credit cards).
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Both numeric and string candidates are accepted.
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"""
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if not isinstance(candidate, basestring):
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candidate = str(candidate)
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try:
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evens = sum([int(c) for c in candidate[-1::-2]])
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odds = sum([LUHN_ODD_LOOKUP[int(c)] for c in candidate[-2::-2]])
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return ((evens + odds) % 10 == 0)
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except ValueError: # Raised if an int conversion fails
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return False
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