title: Setup.py: How to add external installation candidates?
body: <p>I want to configure my <code>setup.py</code> file for a proper installation. Packages and programs which
  are available through PYPI are no problem thanks to the parameter <code>install_requires</code>. Additionally I need to deploy external packages like <code>xvfb</code>.</p>
  
  <p>Can you recommend me a way how to add external dependencies / packages / programs to my 
  <code>setup.py</code> installation?</p>
  
  <p><strong>My current setup.py file</strong></p>
  
  <pre><code>from setuptools import setup, find_packages
  
  setup(
      name = 'package_name',
      version = '0.3.1',
      packages = find_packages('src'),
      package_dir={'':'src'},
      install_requires=['selenium', 'nose',])
  </code></pre>
  
  <p><strong>EDIT:</strong> The goal is to create an installation skript which installs the required packages and the external candidates like this:</p>
  
  <pre><code>&gt;&gt;&gt; sudo python setup.py install 
  # installs selenium, nose and for instance xvfb through e.g. apt-get.
  </code></pre>