title: How can I remove unused packages from virtualenv?
body: <p>How can I keep track of the packages when I install them using pip inside a virtualenv?</p>
  
  <p>It seems like a mess now; if I install package A, it automatically install its dependancies; B, C and D. Then I decide to use package N instead which installs its dependancies as well.</p>
  
  <p>Now when I remove package A, its dependancies are not automatically removed.</p>
  
  <p>How I can keep my virtualenv clean? Is there a tool to check for unused packages and remove them?</p>