title: pip : was OK for months now :ImportError: No module named 'pip._vendor.requests.adapters'
body: <p>All ok until now; Using Win10, Anaconda dstribution, attempting to run pip leads to :  </p>
  
  <pre><code>traceback (most recent call last):
    File "C:\Users\Tim\Anaconda3\Scripts\pip-script.py",
    line    from pip import main  
    File "C:\Users\Tim\Anaconda3\lib\site-packages\pip\__init_    from pip.vcs import git, mercurial, subversion, bazaar  
    File "C:\Users\Tim\Anaconda3\lib\site-packages\pip\vcs\mer    from pip.download import path_to_url  
    File "C:\Users\Tim\Anaconda3\lib\site-packages\pip\downloa    from pip._vendor.requests.adapters import BaseAdapter, 
    H mportError: No module named 'pip._vendor.requests.adapters'
  </code></pre>