fidzu : django

In almost all my Python projects, I'm using pre-commit to handle/check formatting and linting. The advantage: pre-commit is the only tool you need to install. Pre-commit itself reads its config file and installs the formatters and linters you defined in there.

Here's a typical .pre-commit-config.yaml:

default_language_version:
  python: python3

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v6.0.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml
        args: [--allow-multiple-documents]
      - id: check-toml
      - id: check-added-large-files
  - repo: https://github.com/astral-sh/ruff-pre-commit
    # Ruff version.
    rev: v0.15.6
    hooks:
      # Run the linter.
      - id: ruff
        args: ["--fix"]
      # Run the formatter.
      - id: ruff-format
  - repo: https://github.com/tombi-toml/tombi-pre-commit
    rev: v0.9.6
    hooks:
      - id: tombi-format
        args: ["--offline"]
      - id: tombi-lint
        args: ["--offline"]

The "tombi" at the end might be a bit curious. There's already the build-in "check-toml" toml syntax checker, right? Well, tombi also does formatting and schema validation. And in a recent project, I handled configuration through toml files.

It was for a Django website where several geographical maps were shown, each with its own title, description, legend yes/no, etcetera. I made up a .toml configuration format so that a colleague could configure all those maps without needing to deal with the python code. I created a json schema as format specification (yes, json is funnily used for that purpose). With tombi, I could make sure the config files were valid.

Oh, and tombi has an LSP plugin, so I my colleague got autocomplete and syntax help out of the box. nice.

I'm also using uv a lot. That generates an uv.lock file, in .toml format, with all the version pins. It is a toml file, but without the .toml extension. So pre-commit ignored it. Until suddenly it started complaining about the indentation. But only in a github action, not locally.

Note: the complaint about the indentation is probably correct, as there's an issue in the uv bugtracker about changing the indentation from 4 to 2 in the lockfile.

The weird thing for me was that I pin the the versions of the plugins. So the behaviour locally and on github should be the same. Some observations:

• Running tombi from the commandline on uv.lock resulted in re-formatting to two spaces, whatever the tombi version.
• Pre-commit locally did not re-format the file, but pre-commit on the server did.
• I tried it with the new rust-based alternative for pre-commit, prek (see https://github.com/j178/prek), which did re-format uv.lock.

Some further debugging showed that pre-commit was actually skipping the uv.lock file. But apparently not on github. I did some searching in pre-commit's source code and tombi's pre-commit hook definition. The only relevant part there was types: [toml]. So somehow pre-commit has a definition of what a toml file is. But I couldn't find anything.

Until I spotted that pre-commit uses identify as the means to detect file types. (Looks like a handy library, btw!). And that project had a change a couple of weeks ago that identifies uv.lock as a toml file!

• My colleague updated his pre-commit installation and yes: uv.lock was getting re-formatted.
• So: github actions had a newer version than we had.
• Weird, as I just updated my python tool install this morning. Ah: I installed it with homebrew instead of uv tool, that's why it is still older.

Anyway: small mystery solved.