Test failures in jack-of-none

[takluyver]

Notebook tests are failing, but I think #332 in this repo is a more likely culprit than any recent changes in the notebook. Here's the full log, and the bit that looks most likely to be relevant:

Traceback (most recent call last):
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/traitlets/traitlets.py", line 505, in get
    value = obj._trait_values[self.name]
KeyError: 'pre_save_hook'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/base/handlers.py", line 459, in wrapper
    result = yield gen.maybe_future(method(self, *args, **kwargs))
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/tornado/gen.py", line 1015, in run
    value = future.result()
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/tornado/concurrent.py", line 237, in result
    raise_exc_info(self._exc_info)
  File "<string>", line 3, in raise_exc_info
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/tornado/gen.py", line 1021, in run
    yielded = self.gen.throw(*exc_info)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/services/contents/handlers.py", line 214, in post
    yield self._copy(copy_from, path)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/tornado/gen.py", line 1015, in run
    value = future.result()
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/tornado/concurrent.py", line 237, in result
    raise_exc_info(self._exc_info)
  File "<string>", line 3, in raise_exc_info
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/tornado/gen.py", line 285, in wrapper
    yielded = next(result)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/services/contents/handlers.py", line 153, in _copy
    model = yield gen.maybe_future(self.contents_manager.copy(copy_from, copy_to))
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/services/contents/manager.py", line 405, in copy
    model = self.save(model, to_path)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/services/contents/filemanager.py", line 414, in save
    self.run_pre_save_hook(model=model, path=path)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/services/contents/manager.py", line 108, in run_pre_save_hook
    if self.pre_save_hook:
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/traitlets/traitlets.py", line 535, in __get__
    return self.get(obj, cls)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/traitlets/traitlets.py", line 514, in get
    value = self._validate(obj, dgen(obj))
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/traitlets/traitlets.py", line 572, in _validate
    value = self._cross_validate(obj, value)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/traitlets/traitlets.py", line 578, in _cross_validate
    value = obj._trait_validators[self.name](obj, proposal)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/traitlets/traitlets.py", line 897, in __call__
    return self.func(*args, **kwargs)
  File "/var/lib/jenkins/shiningpanda/jobs/92f5a430/virtualenvs/d41d8cd9/lib/python3.4/site-packages/notebook/services/contents/manager.py", line 103, in _validate_pre_save_hook
    raise TraitError("pre_save_hook must be callable")
traitlets.traitlets.TraitError: pre_save_hook must be callable

[rmorshea]

@takluyver, my best guess:

Before #332, "invalid" default values could be defined by leveraging the fact that defaults assigned via a trait's constructor where never cross-validated.

In the case of pre_save_hook, the constructor's default is None, which now raises an error because None is being cross-validated.

[rmorshea]

@takluyver I suspect that similar errors may crop up elsewhere in jupyter, but in my view, these "invalid" defaults were an exploit.

[takluyver]

Yup, I agree that this was really exposing a bug in the notebook. Though we could argue that if the default is None then allow_none should default to True. But I don't think that's terribly important.

[rmorshea]

@takluyver, defaulting to allow_none=True is actually something I've suggested in #315.

[minrk]

I think Any should allow None by default, anyway.

[SylvainCorlay]

I think that we should have

• Any default to None.
• Require a specified default value for Type.
• Require a specified default value for Instance and if not, attempt to construct an instance of the specified type with no argument for the constructor. (i.e. Instance(Foobar) defaults to Foobar())