/docs/guides/introducing_black_to_your_project.md

Introducing Black to your project

This guide is incomplete. Contributions are welcomed and would be deeply appreciated!

Avoiding ruining git blame

A long-standing argument against moving to automated code formatters like Black is that the migration will clutter up the output of git blame. This was a valid argument, but since Git version 2.23, Git natively supports ignoring revisions in blame with the --ignore-rev option. You can also pass a file listing the revisions to ignore using the --ignore-revs-file option. The changes made by the revision will be ignored when assigning blame. Lines modified by an ignored revision will be blamed on the previous revision that modified those lines.

So when migrating your project's code style to Black, reformat everything and commit the changes (preferably in one massive commit). Then put the full 40 characters commit identifier(s) into a file usually called .git-blame-ignore-revs at the root of your project directory.

# Migrate code style to Black
5b4ab991dede475d393e9d69ec388fd6bd949699

Afterwards, you can pass that file to git blame and see clean and meaningful blame information.

$ git blame important.py --ignore-revs-file .git-blame-ignore-revs
7a1ae265 (John Smith 2019-04-15 15:55:13 -0400 1) def very_important_function(text, file):
abdfd8b0 (Alice Doe  2019-09-23 11:39:32 -0400 2)     text = text.lstrip()
7a1ae265 (John Smith 2019-04-15 15:55:13 -0400 3)     with open(file, "r+") as f:
7a1ae265 (John Smith 2019-04-15 15:55:13 -0400 4)         f.write(formatted)

You can even configure git to automatically ignore revisions listed in a file on every call to git blame.

$ git config blame.ignoreRevsFile .git-blame-ignore-revs

The one caveat is that some online Git-repositories do not yet support ignoring revisions using their native blame UI. So blame information will be cluttered with a reformatting commit on those platforms. However, GitHub and GitLab (since version 17.10) both support .git-blame-ignore-revs in blame views by default.