Ubuntu 16.04.04。因为从Ubuntu 16.04.03开始（之前版本没问题的）pip3 install命令必须使用sudo或su才能安装，所以我现在已经将$home/.local/bin加入path，并使用pip3 install *** --user来安装。
最近重做系统，安装theano的时候发现必须安装libgpuarray：有sudo make install和python setup.py install --user命令。
随后，现在发现，无论是pip3 --version还是pip3 install [--user]，都必须使用su权限才可以（sudo也不行），否则错误如下：

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/pip/_vendor/__init__.py", line 33, in vendored
    __import__(vendored_name, globals(), locals(), level=0)
ImportError: No module named 'pip._vendor.pkg_resources'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    from pip import main
  File "/usr/lib/python3/dist-packages/pip/__init__.py", line 13, in <module>
    from pip.exceptions import InstallationError, CommandError, PipError
  File "/usr/lib/python3/dist-packages/pip/exceptions.py", line 6, in <module>
    from pip._vendor.six import iteritems
  File "/usr/lib/python3/dist-packages/pip/_vendor/__init__.py", line 75, in <module>
    vendored("pkg_resources")
  File "/usr/lib/python3/dist-packages/pip/_vendor/__init__.py", line 36, in vendored
    __import__(modulename, globals(), locals(), level=0)
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2927, in <module>
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2913, in _call_aside
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2952, in _initialize_master_working_set
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 956, in subscribe
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2952, in <lambda>
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2515, in activate
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2097, in declare_namespace
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2047, in _handle_ns
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 2066, in _rebuild_mod_path
AttributeError: '_NamespacePath' object has no attribute 'sort'

请问如何解决？