'Raises a ValueError if the choice attribute is missing or invalid.'

def _validate_options(self):

    valid_choices = ('correct', 'partially-correct', 'incorrect')
    for option in self.options:
        choice = option['choice']
        if (choice is None):
            raise ValueError('Missing    required    choice    attribute.')
        elif (choice not in valid_choices):
            raise ValueError('Invalid    choice    attribute:    {0}.    Must    be    one    of:    {1}'.format(choice, ',    '.join(valid_choices)))
