title: "ImportError: cannot import name main" after upgrading to pip 10.0.0 for Python version 2.7.12 - Only one version of Python is installed
body: <p>I got a message in my terminal while install a software : <code>You are using pip version 8.1.1, however version 10.0.0 is available. You should consider upgrading via the 'pip install --upgrade pip' command.</code></p>
  
  <p>So I upgraded pip version: <code>$ pip install --upgrade pip</code></p>
  
  <p>Now I am getting this error: </p>
  
  <pre><code>~$ pip install ipython
  Traceback (most recent call last):
    File "/usr/bin/pip", line 9, in &lt;module&gt;
      from pip import main
  ImportError: cannot import name main
  </code></pre>