title: Too many different Python versions on my system and causing problems
body: <p>During the past years, I have installed many Python libraries with various Python versions. To make them ready to work immediately, I installed them blindly without control. Currently they're causing problems when I tried to install <a href="http://nest-initiative.org/index.php/Software%3aDocumentation">pynest</a> which invokes numpy, scipy and matplotlib. After struggling, I am going to clean and reinstall Python and the libraries.</p>
  
  <p>After investigation, I found Python 2.5/2.6/2.7/3.2 on my system, and each of them has some copies or other things at: (my OS == <strong>Mac OS X 10.7.5 Lion</strong>)</p>
  
  <ul>
  <li><code>/Library/Frameworks/</code></li>
  <li><code>/opt/local/Library/Frameworks/</code></li>
  <li><code>/opt/local/bin/</code></li>
  <li><code>/Applications/</code></li>
  <li><code>/usr/local/bin/</code> </li>
  <li><code>/usr/bin/</code></li>
  <li><code>/System/Library/Frameworks/</code></li>
  </ul>
  
  <p>I know I'm crazy to have these. Now I have removed all these except the things in <code>/System/Libarary/Frameworks</code> (I never remove any thing from <code>/System/Library/</code>). After the clean work, <code>which python</code> now gives <code>/usr/bin/python</code> which links to <code>/System/Library/Frameworks</code>. </p>
  
  <p>Now, is it a clear environment for me to reinstall python? How to double check that there's no other versions existing? How should I reinstall them to guarantee that they and their libraries won't be everywhere and have many copies again? </p>
  
  <p>I want to install a clean Python 2.7 onto a proper location, and make my system know exactly where it is and never install any libraries somewhere else. Please give me some advice that how to manage it like in a professional way.</p>
  
  <p>For your information, here is my current <code>$PATH</code>, I think it should be modified:</p>
  
  <pre><code>/opt/local/bin:/opt/local/sbin:/opt/nest/lib/python2.7/site-packages:/usr/local/lib/python2.7/site-packages:/Library/Frameworks/Python.framework/Versions/2.7/bin:/usr/texbin:/Library/Frameworks/Python.framework/Versions/3.2/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/texbin:/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/django/bin:/usr/X11/bin:/opt/local/bin:/opt/local/sbin:/usr/local/lib/python2.7/site-packages:/Library/Frameworks/Python.framework/Versions/2.7/bin:/Library/Frameworks/Python.framework/Versions/3.2/bin
  </code></pre>
  
  <p>Please let me know If you need more information. Thank you!</p>
  
  <hr>
  
  <p><strong>UPDATE</strong>:</p>
  
  <p>I'm rethinking profoudly why it becomes so crazy. I believe it's because I installed things via:</p>
  
  <ul>
  <li><code>easy_install</code> / <code>macports</code> / <code>homebrew</code> / <code>fink</code> / <code>pip</code> sometimes;</li>
  <li><code>.dmg</code> sometimes; </li>
  <li><code>.pkg</code> sometimes;</li>
  <li>compile source code sometimes;</li>
  </ul>
  
  <p>and they made things at different locations. I wonder what's the mechanism behind these ways? How do they choose target location? How to prevent them from messing things up?   </p>