A
diff is the differences between two files. This is essential for knowing the exact differences between two files. If we manually look at two files side by side it may happen that we miss small subtleties, so it serves us better to leave that job to a much more strict eye: software. The following gist is probably self explanatory. The difflib is perhaps an obscure module, worth exploring. If GAE supports difflib I will write a diff generator at some point (one that offers a download generated clientside)
This version would write the diff to disk:
