title: How do I force a new version of Django in a virtualenv?
body: <p>I want to install <strong>version 1.3.1</strong> of Django in a new virtualenv. I already have Django version 1.3.0 installed system-wide. I have installed the virtualenv with <code>no-site-packages</code> and attempted to reinstall Django as follows, but with no success:</p>
  
  <pre><code>$ virtualenv --no-site-packages pyenv
  New python executable in pyenv/bin/python
  Installing setuptools............done.
  Installing pip...............done.
  $ source pyenv/bin/activate
  (pyenv)$ python
  Python 2.6.6 (r266:84292, May 26 2011, 21:27:16) 
  [GCC 4.2.1 (Apple Inc. build 5664)] on darwin
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; import django
  &gt;&gt;&gt; django.VERSION
  (1, 3, 0, 'final', 0)
  </code></pre>
  
  <p>OK, so even though I haven't installed Django and I have used <code>no-site-packages</code>, the virtualenv has still somehow picked up the system version.</p>
  
  <p>Now to try to over-write it with version 1.3.1:</p>
  
  <pre><code>(pyenv)$ pip install django==1.3.1
  Downloading/unpacking django==1.3.1
    Downloading Django-1.3.1.tar.gz (6.5Mb): 6.5Mb downloaded
    Running setup.py egg_info for package django
  Installing collected packages: django
    Found existing installation: Django 1.3
      Not uninstalling Django at /opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages, outside environment /Users/anna/Dropbox/code-local/pyenv/pyenv/bin/..
    Running setup.py install for django
      changing mode of build/scripts-2.6/django-admin.py from 644 to 755
      changing mode of /Users/anna/Dropbox/code-local/pyenv/pyenv/bin/django-admin.py to 755
  Successfully installed django
  Cleaning up...
  (pyenv)$ python
  Python 2.6.6 (r266:84292, May 26 2011, 21:27:16) 
  [GCC 4.2.1 (Apple Inc. build 5664)] on darwin
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; import django
  &gt;&gt;&gt; django.VERSION
  </code></pre>
  
  <p>That hasn't worked, it's still pointing at 1.3.0! </p>
  
  <p>Note the line: <code>Found existing installation: Django 1.3 Not uninstalling Django</code>. </p>
  
  <p>How can I force my virtualenv to use 1.3.1? Do I need to edit my local Python path?</p>
  
  <p>I'm confused as to why the virtualenv can even see the system Django when I've explicitly installed with <code>no-site-packages</code>. Is this how it's supposed to work?</p>