app/django/utils/checksums.py
author Todd Larsen <tlarsen@google.com>
Mon, 27 Oct 2008 19:19:44 +0000
changeset 426 114fe0f840c8
parent 54 03e267d67478
permissions -rw-r--r--
Add tooltips style display of help_text, instead of widening the form with another (often ridiculously large) column. Also, version the .css and .js files so that browsers won't display the wrong cached one when we change something. Patch by: Dmitri Gaskin, Todd Larsen Review by: Todd Larsen
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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