Define the Models for implementing Quizzes (collections of Questions) and their Responses (collections of Answers to those Questions). These Models would form the basis of storage for such items as: Terms of Service (Quiz) Question ("I agree...") Response -> Answer (answer to "I agree..." confirmation) solution ("Yes" Answer to the "I agree..." Question) Mentor and Student surveys (Quiz) Questions (including "Pay this student?") Response -> Answers solution ("Yes" Answer to the "Pay this student?" Question) Organization applications Student Proposal review, comment, and scoring system GHOP task tracking (a specific task list item would be a Quiz) Patch by: Todd Larsen Review by: Pawel Solyga, Sverre Rabbelier, Chen Lunpeng Review URL: http://codereviews.googleopensourceprograms.com/1403

"""
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