title: Prompt user for file input
body: <p>I have code that manipulates data of a file that I currently have hard-coded in the script.  I want to be able to prompt the user to chose the input file rather than having to hard-code it.  Here is what I have for input.  Instead of always using myfile.txt, I'd like the user to be able to choose the file:</p>
  
  <pre><code>with open('myfile.txt', 'rU') as input_file:
  </code></pre>