ModuleNotFoundError: No module named 'attr'

jupyter notebook을 실행하니 다음과 같은 오류가 떴다.

Traceback (most recent call last):
File "/home/ubuntu/Downloads/anaconda3/bin/jupyter-notebook", line 7, in
from notebook.notebookapp import main
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/notebook/notebookapp.py", line 80, in
from .services.contents.manager import ContentsManager
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/notebook/services/contents/manager.py", line 17, in
from nbformat import sign, validate as validate_nb, ValidationError
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/nbformat/init.py", line 32, in
from .validator import validate, ValidationError
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/nbformat/validator.py", line 12, in
from .json_compat import get_current_validator, ValidationError
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/nbformat/json_compat.py", line 10, in
import jsonschema
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/jsonschema/init.py", line 11, in
from jsonschema.exceptions import (
File "/home/ubuntu/Downloads/anaconda3/lib/python3.8/site-packages/jsonschema/exceptions.py", line 9, in
import attr
ModuleNotFoundError: No module named 'attr'

jupyter notebook을 재설치하면 해결된다.