Error launching Jupyter lab in new environment

Question

After creating a new environment in Anaconda I installed Jupyter lab through the navigator. When I try to run, the following error message appears:

C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\notebookapp.py:73: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
_("Don't open the notebook in a browser after startup.")
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\notebookapp.py:89: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
_("Allow the notebook to be run from root user.")
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:20: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_('Deprecated: Use minified JS file or not, mainly use during dev to avoid JS recompilation'),
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:25: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("Supply extra arguments that will be passed to Jinja environment."))
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:29: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("Extra variables to supply to jinja templates when rendering."),
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:62: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("""Path to search for custom.js, css""")
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:74: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("""Extra paths to search for serving jinja templates.
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:85: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("""extra paths to look for Javascript notebook extensions""")
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:130: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("""The MathJax.js configuration file that is to be used.""")
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\traits.py:143: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=(_("Dict of Python modules to load as notebook server extensions."
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\notebookapp.py:122: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
description = _("""The Jupyter HTML Notebook.
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\notebookapp.py:143: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("""Path to search for custom.js, css""")
C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\notebookapp.py:155: FutureWarning: The alias `_()` will be deprecated. Use `_i18n()` instead.
help=_("""extra paths to look for Javascript notebook extensions""")
[I 2022-02-13 18:11:53.842 ServerApp] jupyterlab | extension was successfully linked.
[W 2022-02-13 18:11:54.449 ServerApp] 'ExtensionManager' object has no attribute '_extensions'
Traceback (most recent call last):
File "C:\ProgramData\Anaconda3\envs\Environment_1\Scripts\jupyter-lab-script.py", line 9, in 
sys.exit(main())
File "C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\jupyter_server\extension\application.py", line 567, in launch_instance
serverapp = cls.initialize_server(argv=args)
File "C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\jupyter_server\extension\application.py", line 537, in initialize_server
serverapp.initialize(
File "C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\traitlets\config\application.py", line 88, in inner
return method(app, *args, **kwargs)
File "C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\jupyter_server\serverapp.py", line 2341, in initialize
point = self.extension_manager.extension_points[starter_extension]
File "C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\jupyter_server\extension\manager.py", line 303, in extension_points
for value in self.extensions.values()
File "C:\ProgramData\Anaconda3\envs\Environment_1\lib\site-packages\nbclassic\nbserver.py", line 80, in extensions
nb = self._extensions.get("nbclassic")
AttributeError: 'ExtensionManager' object has no attribute '_extensions'

I've found the same error in some SO questions which all pointed me to this Github issue, which suggests that an updated verison of nbclassic should solve it. I tried to install the latest version (actually it seems it was already installed when creating the environment) but the error persists.

Any suggestion?

Answer 1

I had the same error message attempting to run jupyter lab today after updating everything on Anaconda. It did not affect jupyter notebook, so that may still work regardless.

What worked for me was running the following:

conda install -c conda-forge nbclassic=0.2.8 

Previously I tried the advice of others which had recommended:

conda install -c conda-forge nbclassic>=0.2.8 

It seems that version 0.2.8 works, however the current version (0.3.5) of nbclassic may be causing the error. Rolling back to 0.2.8 may also work for you.