title: How to specify versions on PIP when installing a python package with it's dependencies
body: <p>To install Celery with it's redis dependencies, one can do this.</p>
  
  <pre><code>$ pip install celery[redis]
  </code></pre>
  
  <p>Is it possible to explicitly provide version numbers to both celery and redis in the above command? It will effectively be the same as the following two commands</p>
  
  <pre><code>$ pip install -Iv redis==2.10.3
  $ pip install -Iv celery==3.1.18
  </code></pre>