title: Quickly find differences between two large text files
body: <p>I have two 3GB text files, each file has around 80 million lines. And they share 99.9% identical lines (file A has 60,000 unique lines, file B has 80,000 unique lines).</p>
  
  <p>How can I quickly find those unique lines in two files? Is there any ready-to-use command line tools for this? I'm using Python but I guess it's less possible to find a efficient Pythonic method to load the files and compare.</p>
  
  <p>Any suggestions are appreciated.</p>