安装nbextensions后jupyter根本不会运行

Question

尝试安装nbextensions之后，jupyter根本无法运行。我收到以下消息：

 File "/Users/briantaylor/anaconda/bin/jupyter-notebook", line 7, in <module>
    from notebook.notebookapp import main
  File "/Users/briantaylor/anaconda/lib/python3.5/site-packages/notebook/__init__.py", line 25, in <module>
    from .nbextensions import install_nbextension
  File "/Users/briantaylor/anaconda/lib/python3.5/site-packages/notebook/nbextensions.py", line 27, in <module>
    from jupyter_core.utils import ensure_dir_exists
ImportError: cannot import name 'ensure_dir_exists'