def subtract(self, iterable=None, **kwds):
        if iterable is not None:
            self_get = self.get
            if isinstance(iterable, Mapping):
                for elem, count in iterable.items():
                    self[elem] = self_get(elem, 0) - count
            else:
                for elem in iterable:
                    self[elem] = self_get(elem, 0) - 1
        if kwds:
            self.subtract(kwds)
If verification credentials are bad, an error is raised
dataset/ETHPy150Open Exa-Networks/exabgp/lib/exabgp/dep/counter.py/Counter.subtract--crossover with--dataset/ETHPy150Open freakboy3742/pyxero/tests/auth.py/PublicCredentialsTest.test_verify_failure