35 lines
988 B
Python
35 lines
988 B
Python
"""
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Common checksum routines.
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"""
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__all__ = ['luhn']
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import warnings
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from django.utils import six
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from django.utils.deprecation import RemovedInDjango20Warning
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warnings.warn(
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"django.utils.checksums will be removed in Django 2.0. The "
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"luhn() function is now included in django-localflavor 1.1+.",
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RemovedInDjango20Warning
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)
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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, six.string_types):
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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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