title: Changing which Python version pip points to
body: <p>I am using python2.7 and python3.5 on Ubuntu 16.04. After upgrading pip to v10 I am no longer able to install packages for python2.7 using pip.</p>
  
  <p>How can I change pip to point to python2.7?</p>
  
  <pre><code>$ pip -V
  pip 10.0.0 from /home/username/.local/lib/python3.5/site-packages/pip (python 3.5)
  
  $ pip3 -V
  pip 10.0.0 from /home/username/.local/lib/python3.5/site-packages/pip (python 3.5)
  
  $ which python
  /usr/bin/python
  
  $ which python3
  /usr/bin/python3
  
  $ python -V
  Python 2.7.12
  
  $ python3 -V
  Python 3.5.2
  
  $ which pip
  /usr/local/bin/pip
  
  $ which pip3
  /usr/local/bin/pip3
  
  $ python3 -m pip install some_module
  $ python -m pip install some_module
  </code></pre>
  
  <p><code>python/python3 -m pip install some_module</code> both installs to python 3.5.</p>
  
  <p>Using Anaconda is not an option.</p>