执行Jupyter Notebook时出错：ImportError：无法导入名称'_RuleList'

Question

当我执行jupyter notebook命令时，我得到

 jupyter notebook
Traceback (most recent call last):
  File "/usr/local/bin/jupyter-notebook", line 6, in <module>
    from notebook.notebookapp import main
  File "/usr/local/lib/python3.6/dist-packages/notebook/notebookapp.py", line 63, in <module>
    from tornado import web
  File "/usr/local/lib/python3.6/dist-packages/tornado/web.py", line 95, in <module>
    from tornado.routing import (
ImportError: cannot import name '_RuleList'
(my_project_env)