title: How can I upgrade specific packages using pip and a requirements file?
body: <p>I'm using pip with a requirements file, in a virtualenv, for my Django projects.  I'm trying to upgrade some packages, notably Django itself, and I'm getting an error about source code conflicts:</p>
  <blockquote>
  <p>Source in <code>&lt;virtualenv</code>&gt;/build/Django has version 1.2.3 that conflicts with Django==1.2.4 (from -r requirements/apps.txt (line 3))</p>
  </blockquote>
  <p>That's after updating the version number of Django from 1.2.3 to 1.2.4 in my requirements file.  I'm using this command to actually do the upgrade:</p>
  <pre><code>pip --install --upgrade -E `&lt;virtualenv dir`&gt; --requirement `&lt;requirements file`&gt;
  </code></pre>
  <p>I can't find any flag that triggers a total package re-download.  I even tried running an uninstall command first, and then the install, but no dice. Am I missing something?</p>