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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 |