"This should be unreachable" error message hard to interpret

[yaroslavvb]

I've seen this when forgetting to call ray.init(), maybe it should say ..Unreachable...Did you call ray.init()?

    return func(*args, **kwargs)
  File "/home/ubuntu/Dropbox/git0/tensorpack/tensorpack/train/base.py", line 253, in main_loop
    self.run_step()  # implemented by subclass
  File "resnet_numpy_concat_ray_test.py", line 184, in run_step
    ps = ParameterServer.remote(grad_values_flat.size)
  File "/home/ubuntu/anaconda3/envs/mxnet_p36/lib/python3.6/site-packages/ray/actor.py", line 761, in remote
    ray.worker.global_worker)
  File "/home/ubuntu/anaconda3/envs/mxnet_p36/lib/python3.6/site-packages/ray/actor.py", line 387, in export_actor_class
    assert False, "This should be unreachable."