title: Unable to install nltk in a virtual environment?
body: <p>After activating the virtual environment, when I try:</p>
  
  <pre><code>$ sudo pip install -U nltk
  </code></pre>
  
  <p>it shows this message:</p>
  
  <blockquote>
    <p>Requirement already up-to-date: nltk in /usr/local/lib/python2.7/dist-packages</p>
  </blockquote>
  
  <p>Why isn't it downloading those packages?
  Should I use --no-site-packages while activating?</p>