每次pip安装尝试导入错误：DependencyWarning

Question

我是一名mac用户，并使用pip进行安装。但是我做了一些事情，现在它不再起作用了。运行pip install somepackagename时，我收到错误ImportError: cannot import name DependencyWarning。我粘贴了下面的整个错误，试图安装PyPDF2。

据我所知，错误与requests模块有关。我试图卸载它运行pip卸载请求，这会导致相同的错误。也卸载其他软件包。

有人知道出了什么问题吗？

安装PyPDF2时的错误

Traceback (most recent call last):
  File "/Users/Arno/Library/Enthought/Canopy_64bit/User/bin/pip", line 9, in <module>
    load_entry_point('pip==7.1.2', 'console_scripts', 'pip')()
  File "/Users/Arno/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pkg_resources/__init__.py", line 558, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/Users/Arno/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2682, in load_entry_point
    return ep.load()
  File "/Users/Arno/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2355, in load
    return self.resolve()
  File "/Users/Arno/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2361, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/Users/Arno/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pip/__init__.py", line 22, in <module>
    from pip._vendor.requests.packages.urllib3.exceptions import DependencyWarning
ImportError: cannot import name DependencyWarning