title: Calling command line arguments in Python 3
body: <p>I am writing a program in Python 3 that will take data from a csv file, make adjustments to it and write the new data to a csv file that will be named by the user.</p>
  
  <p>I'm just trying to understand the command line part.
  I want it to execute properly in this format.</p>
  
  <pre><code>$ program.py input.csv output.csv
  </code></pre>
  
  <p>I plan to also make it check that there are 3 total arguments.</p>
  
  <p>My question is where do this filename inputs on the command line go?
  Are they saved to a default variable? How can I call these filenames within my python program?</p>