Ошибка при установке & ldquo; sudo pip install -V protobuf == 3.0.0a2 & rdquo;

Когда я хочу установить protobuf, я набрал команду: pip install -V protobuf==3.0.0a2, затем я получил следующие результаты:

Traceback (most recent call last):
File "/usr/local/bin/pip", line 9, in <module>
load_entry_point('pip==8.1.1', 'console_scripts', 'pip')()
  File "/usr/local/lib/python2.7/dist-packages/setuptools-5.7-py2.7.egg/pkg_resources.py", line 356, in load_entry_point
  File "/usr/local/lib/python2.7/dist-packages/setuptools-5.7-py2.7.egg/pkg_resources.py", line 2472, in load_entry_point
  File "/usr/local/lib/python2.7/dist-packages/setuptools-5.7-py2.7.egg/pkg_resources.py", line 2186, in load
  File "/usr/lib/python2.7/dist-packages/pip/__init__.py", line 18, in <module>
    from pip.commands import get_summaries, get_similar_commands
  File "/usr/lib/python2.7/dist-packages/pip/commands/__init__.py", line 8, in <module>
    from pip.commands.freeze import FreezeCommand
  File "/usr/lib/python2.7/dist-packages/pip/commands/freeze.py", line 8, in <module>
    from pip.operations.freeze import freeze
  File "/usr/lib/python2.7/dist-packages/pip/operations/freeze.py", line 11, in <module>
    from pip._vendor.pkg_resources import RequirementParseError
 ImportError: cannot import name RequirementParseError

Кто-нибудь знает, как ее решить?