title: Compare two text files and return the difference (case insensitive)
body: <p>I'm new to Python programming so forgive me if my code is not efficient, etc. I need to compare text file B with text file B and print the results out to another file. Simply put, result C = text file A - text file B. </p>
  
  <p>I have the following code which works, however, there are duplicate results due to upper and lower cases. How can I make it such that my program can compare it without case sensitivity?</p>
  
  <pre><code>#!/usr/local/bin/python -u
  
  file1='A_GAGL.txt'
  file2='B_GGL.txt'
  
  def key(line):
    return tuple(line.strip().split()[0:2])
  
  def make_key_set(file_path):
    return set(key(line) for line in open(file_path))
  
  
  def filtered_lines(file_path1, file_path2):
    key_set = make_key_set(file_path2)
    return (line for line in open(file_path1) if key(line) not in key_set)
  
  if __name__ == "__main__":
    file3 = open("file4.txt", "w")
    for line in filtered_lines(file1, file2):
        file3.write(line)
    file3.close()
  </code></pre>
  
  <p>Many thanks in advance</p>