我使用pip安装了ipynotebook并且每次尝试使用终端启动ipython notebook时都会出现此错误（ubuntu 14.04）
siddharth@siddharth-HP-Pavilion-g6-Notebook-PC:~$ ipython notebook
Traceback (most recent call last): File "/usr/local/bin/ipython", line 7, in <module> from IPython import start_ipython File "/usr/local/lib/python2.7/dist-packages/IPython/__init__.py", line 47, in <module> from .core.application import Application File "/usr/local/lib/python2.7/dist-packages/IPython/core/application.py", line 22, in <module> from traitlets.config.application import Application, catch_config_error File "/usr/local/lib/python2.7/dist-packages/traitlets/config/__init__.py", line 6, in <module> from .application import * File "/usr/local/lib/python2.7/dist-packages/traitlets/config/application.py", line 17, in <module> from decorator import decorator ImportError: No module named decorator
我该怎么办？