title: Multiple python versions: How to set default python binary
body: <p>I have installed python 2.7.5 on CentOS 6.4 which python 2.6 already installed.</p>
  
  <p>Python2.7 is under /usr/local/bin and library configuration is correct as well.</p>
  
  <p>I set alias in .bash_profile as </p>
  
  <pre><code>alias python='/usr/local/bin/python2.7'
  PATH=$PATH:/usr/local/bin
  </code></pre>
  
  <p>However, I need to do <code>source .bash_profile</code> each time I logged in and it's pretty annoying.
  How can I change my default python version to python2.7.5?</p>
  
  <p>Thanks</p>