title: How to use Python virtualenv
body: <p>The scenario is: I am  on Ubuntu 11 which comes with Python 2.7, I want to run Mozilla JetPack which supports Python 2.5/2.6 and Google App Engine which only supports Python 2.5. </p>
  
  <p>Read that its not a good idea to remove Python 2.7 as Ubuntu maybe using it. So the correct way is to use <code>virtualenv</code>. But I am quite lost using it. I installed Python 2.5 in <code>/usr/local/python25</code> following <strong><a href="http://welcometoubuntu.blogspot.com/2010/05/howto-install-python-255-on-ubuntu-1004.html">this guide</a></strong> </p>
  
  <p>I tried</p>
  
  <pre><code>jiewmeng@JM:/usr/local/python25/bin$ ./python --version
  Python 2.5.5
  jiewmeng@JM:/usr/local/python25/bin$ ./python virtualenv /works/tmp/test
  ./python: can't open file 'virtualenv': [Errno 2] No such file or directory
  </code></pre>
  
  <p>then the below works but I will be using Python 2.7</p>
  
  <pre><code>jiewmeng@JM:/usr/local/python25/bin$ virtualenv /works/tmp/test
  New python executable in /works/tmp/test/bin/python
  Installing distribute.................................................................................................................................................................................done.
  jiewmeng@JM:/usr/local/python25/bin$ cd /works/tmp/test/bin
  jiewmeng@JM:/works/tmp/test/bin$ ls
  activate  activate_this.py  easy_install  easy_install-2.7  pip  python
  jiewmeng@JM:/works/tmp/test/bin$ ./python --version
  Python 2.7.1+
  </code></pre>
  
  <p>Also, how do I then run Mozilla JetPack or Google App Engine with this version of Python? Sorry I am new to Python (and Linux/Ubuntu)</p>