def _is_reference(arg):
    return isinstance(arg, dict) and len(arg) == 1 and isinstance(next(six.itervalues(arg)), six.string_types)
Checks to make sure that the SIN passes a luhn mod-10 checksum
dataset/ETHPy150Open saltstack/salt/salt/modules/syslog_ng.py/_is_reference--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.2/django/contrib/localflavor/ca/forms.py/CASocialInsuranceNumberField.luhn_checksum_is_valid