Jupyter Notebook ImportError:没有名为tornado.log的模块

我已经安装了jupyter，并且尝试启动它时，出现以下错误:

I have installed jupyter and when trying to start it, I get the following error:

File "/Library/Frameworks/Python.framework/Versions/2.7/bin/jupyter-notebook", line 7, in <module>
from notebook.notebookapp import main
File"/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/notebook/__init__.py", line 25, in <module>
from .nbextensions import install_nbextension
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/notebook/nbextensions.py", line 35, in <module>
from tornado.log import LogFormatter
ImportError: No module named tornado.log

我尝试卸载并重新安装jupyter，龙卷风或任何我可以以某种方式链接到此错误的内容，但没有任何帮助.这实际上曾经可以很好地工作，但是最近它开始对我抛出上述错误.任何帮助，我们将不胜感激.

I tried uninstalling and reinstalling jupyter, tornado, or anything I could somehow link to this error and nothing really helped. This actually used to work pretty well but it recently began throw the above error at me. Any help is greatly appreciated.