Jupyter server process finishedTraceback (most recent call last):
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/jsonschema/__init__.py", line 31, in <module>
    from importlib import metadata
ImportError: cannot import name 'metadata' from 'importlib' (/home/wgj/anaconda3/lib/python3.7/importlib/__init__.py)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/wgj/anaconda3/bin/jupyter-notebook", line 7, in <module>
    from notebook.notebookapp import main
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/notebook/notebookapp.py", line 85, in <module>
    from .services.contents.manager import ContentsManager
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/notebook/services/contents/manager.py", line 17, in <module>
    from nbformat import sign, validate as validate_nb, ValidationError
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/nbformat/__init__.py", line 32, in <module>
    from .validator import validate, ValidationError
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/nbformat/validator.py", line 12, in <module>
    from .json_compat import get_current_validator, ValidationError
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/nbformat/json_compat.py", line 10, in <module>
    import jsonschema
  File "/home/wgj/anaconda3/lib/python3.7/site-packages/jsonschema/__init__.py", line 33, in <module>
    import importlib_metadata as metadata
ModuleNotFoundError: No module named 'importlib_metadata'

conda install -c anaconda importlib-metadata