title: Download files from a list if not already downloaded
body: <p>I can do this in c#, and the code is pretty long.  </p>
  
  <p>Would be cool if someone can show me how this would be done via python.</p>
  
  <p>Pseudo code is:</p>
  
  <pre><code>url: www.example.com/somefolder/filename1.pdf
  
  1. load file into an array (file contains a url on each line)
  2. if file e.g. filename1.pdf doesn't exist, download file
  </code></pre>
  
  <p>The script can be in the following layout:</p>
  
  <pre><code>/python-downloader/
  /python-downloader/dl.py
  /python-downloader/urls.txt
  /python-downloader/downloaded/filename1.pdf
  </code></pre>