def get(self, key, default=None):
        try:
            val = self[key]
        except KeyError:
            return default
        if val == []:
            return default
        return val
This method checks if the last letter/digit in value is valid
dataset/ETHPy150Open wcong/ants/ants/utils/datatypes.py/MultiValueDict.get--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/contrib/localflavor/cn/forms.py/CNIDCardField.has_valid_checksum