def challenge(self, challenge, mode='HMAC', slot=1, variable=True, may_block=True):
        pass
write the module-level namespace-generating callable.
dataset/ETHPy150Open Yubico/python-yubico/yubico/yubikey_base.py/YubiKey.challenge--crossover with--dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/mako/codegen.py/_GenerateRenderMethod.write_namespaces