def delete_many(self, *keys):
        if not keys:
            return True
        return all(self.delete(key) for key in keys)
Validates the input and returns a string that contains only numbers.
dataset/ETHPy150Open fengsp/rc/rc/cache.py/BaseCache.delete_many--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/contrib/localflavor/cz/forms.py/CZPostalCodeField.clean