当我尝试用pip或pip3安装任何东西时，我得到:

$ sudo pip3 install python3-tk
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    load_entry_point('pip==1.5.6', 'console_scripts', 'pip3')()
  File "/usr/lib/python3/dist-packages/pkg_resources.py", line 356, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python3/dist-packages/pkg_resources.py", line 2476, in load_entry_point
    return ep.load()
  File "/usr/lib/python3/dist-packages/pkg_resources.py", line 2190, in load
    ['__name__'])
  File "/usr/lib/python3/dist-packages/pip/__init__.py", line 61, in <module>
    from pip.vcs import git, mercurial, subversion, bazaar  # noqa
  File "/usr/lib/python3/dist-packages/pip/vcs/mercurial.py", line 9, in <module>
    from pip.download import path_to_url
  File "/usr/lib/python3/dist-packages/pip/download.py", line 25, in <module>
    from requests.compat import IncompleteRead
ImportError: cannot import name 'IncompleteRead'

我用的是Ubuntu 14.10系统。

我该如何解决这个问题?