All the other responses are more complete, so upvote them. This one is just to remember that you can avoid knowing the id of the recent commit. Usually, I set my self in the branch that I want to compare and run diff tools knowing the old commit uid (You can use other notations):
git checkout master
git difftool 6f8bba my/file/relative/path.py
Also, check this other response here to set the tool you want git open to compare the file: Configuring diff tool with .gitconfig And to learn more about difftool, go to the difftool doc