ModuleNotFoundError: No module named 'jupyter_server.contents'

[Charles-Gagnon]

Version: 6.5.5

I've recently started seeing this error when starting up a Notebook app with package version 6.5.5

import notebook.notebookapp
notebook.notebookapp.main()

File "C:\Users\chgagnon\AppData\Roaming\Python\Python38\site-packages\notebook\traittypes.py", line 235, in _resolve_classes
    klass = self._resolve_string(klass)
  File "C:\Users\chgagnon\AppData\Roaming\Python\Python38\site-packages\traitlets\traitlets.py", line 2009, in _resolve_string
    return import_item(string)
  File "C:\Users\chgagnon\AppData\Roaming\Python\Python38\site-packages\traitlets\utils\importstring.py", line 30, in import_item
    module = __import__(package, fromlist=[obj])
ModuleNotFoundError: No module named 'jupyter_server.contents'

It seems to be caused by #5957. In it there's two similar lines in different files

https://github.com/jupyter/notebook/pull/5957/files#diff-805382c95cfca475b5339bcb7ccd1ee13e9326a9d15adf3a6419d32cb38024d5R1394

This has the type specified as jupyter_server.contents.services.managers.ContentsManager (which doesn't seem to be a valid path)

while in https://github.com/jupyter/notebook/pull/5957/files#diff-ba803f92fc3fea5ab9ef22c8064d587d629353f5c9beaa33a809d70dad8cea80R34

it's specified as jupyter_server.services.contents.manager.ContentsManager

Not sure if I'm missing something, or if this was just a typo but I confirmed that if I go in and manually change the "wrong" name in $(Python)\site-packages\notebook\notebookapp.py to the other name then it seems to start up and everything is fine.

[Charles-Gagnon]

@afshin @kevin-bates @blink1073 FYI since you were involved in the original PR

[Charles-Gagnon]

We've tracked the issue down to the traitlets package. With 5.10.0 we see this issue, if we downgrade to 5.9.0 then it goes away.

[minrk]

This is a typo because it should be jupyter_server.services.contents, not jupyter_server.contents.services, but if updating traitlets is the cause, then traitlets has introduced a breaking change in 5.10 in how it handles classes that don't import in this situation. the bug is purely in notebook, which imported a name not in the traitlets API from traitlets, instead of from the standard library.

[muhammadyaseen]

@Charles-Gagnon Thanks for opening the issue. I am also getting the same error when I run jupyter notebook in the terminal.

  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/notebook/traittypes.py", line 235, in _resolve_classes
    klass = self._resolve_string(klass)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/traitlets.py", line 2009, in _resolve_string
    return import_item(string)
           ^^^^^^^^^^^^^^^^^^^
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/utils/importstring.py", line 30, in import_item
    module = __import__(package, fromlist=[obj])
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
**ModuleNotFoundError: No module named 'jupyter_server.contents'**

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/yaseen/anaconda3/envs/ptenv/bin/jupyter-notebook", line 10, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/jupyter_core/application.py", line 285, in launch_instance
    return super().launch_instance(argv=argv, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/config/application.py", line 1044, in launch_instance
    app = cls.instance(**kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/config/configurable.py", line 555, in instance
    inst = cls(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/traitlets.py", line 1295, in __new__
    inst.setup_instance(*args, **kwargs)
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/traitlets.py", line 1338, in setup_instance
    super(HasTraits, self).setup_instance(*args, **kwargs)
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/traitlets/traitlets.py", line 1314, in setup_instance
    init(self)
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/notebook/traittypes.py", line 226, in instance_init
    self._resolve_classes()
  File "/home/yaseen/anaconda3/envs/ptenv/lib/python3.11/site-packages/notebook/traittypes.py", line 238, in _resolve_classes
    warn(f"{klass} is not importable. Is it installed?", ImportWarning)
TypeError: warn() missing 1 required keyword-only argument: 'stacklevel'

Downgrading traitlets to version 5.9.0 fixes it in my case as well: conda install traitlets==5.9.0 -c conda-forge

[mirekphd]

Related: the buggy / breaking version of traitlets is also installed by jupyter_core so it arguably should be also pinned here:
https://github.com/jupyter/jupyter_core/blob/main/pyproject.toml#L21C4-L21C13

Note that jupyter_core is used by both notebook AND jupyterlab... propagating the bug to both these IDEs.

[blink1073]

For clarity, this is not a bug in traitlets, it is a bug in notebook v6, as @minrk said above.

[Charles-Gagnon]

Verified that fix released in 6.5.6 resolves this issue. Thanks!