Use RemoteTraceback to output the cause of an exception when it is thrown

[stevenheidel]

We're using Pebble and were having difficulty debugging due to the stack trace of the original exception not being shown. The solution I took is the same one that is used in multiprocessing.pool.

Without this change, the information we got by default from an error within a process was something like:
AssertionError

Now we get the full stacktrace:

Traceback (most recent call last):
  File "/Users/steven/.pyenv/versions/3.6.3/lib/python3.6/concurrent/futures/process.py", line 175, in _process_worker
    r = call_item.fn(*call_item.args, **call_item.kwargs)
  File "/Users/steven/workspace/project/low_level_translation.py", line 237, in translate_to_settings
    settings = generate_settings(input)
  File "/Users/steven/workspace/project/low_level_translation.py", line 119, in generate_settings
    assert input.direction == output.direction
AssertionError

[noxdafox]

Thanks for your contribution!

The remote traceback is appended to the exception but it's not documented and I personally don't like it myself. I was planning to refactor it but it was low in my TODO list.

Your solution only covers the ProcessPool use case and not all the use cases (ThreadPool, decorators etc) but it's a good starting point. I will further develop it.

In the meantime, you can access the remote traceback of the error like in this example (check the generic Exception handler).