def get_unique(self, filter_fun):
        """Finds a unique item that satisfies a given filter.

        Returns:
           The item or None if not found.
        """
        result = filter(filter_fun, self.all())
        count = len(result)
        assert 1 <= count
        if count == 0:
            return None
        return result[0]
dataset/ETHPy150Open wrr/wwwhisper/wwwhisper_auth/models.py/Collection.get_unique/swapped operands of `<=`