ruff format (+ isort) を Python から使用できるようにする

Ruff のフォーマッタには Python から使用できる API はないのかと思って探したが、なかった。¹

ないものは作ればよい。

import subprocess
from tempfile import NamedTemporaryFile
from typing import Any


def ruff_format(
    code: str,
    *,
    ruff_command: str = "ruff",
    isort: bool = True,
    line_length: int | None = None,
) -> str:
    run_options: dict[str, Any] = {"text": True, "capture_output": True, "check": True}

    # isort
    if isort:
        with NamedTemporaryFile("w+", suffix=".py") as f:
            f.write(code)
            f.flush()
            cmd = [ruff_command, "check", "--isolated", "--fix"]
            cmd += ["--select", "I"]  # isort
            subprocess.run(cmd + [f.name], **run_options)
            f.seek(0)
            code = f.read()

    # format
    cmd = [ruff_command, "format", "--isolated"]
    if line_length:
        cmd += ["--line-length", str(line_length)]
    code = subprocess.run(cmd + ["-"], input=code, **run_options).stdout

    return code

使用例

from subprocess import CalledProcessError

code = """\
import sys, os
def add(a:int,b:int)->int:
  return a+b
print(add(1,2))
"""
try:
    print(ruff_format(code))
except CalledProcessError as exc:
    print(exc.stdout)

実行結果

import os
import sys


def add(a: int, b: int) -> int:
    return a + b


print(add(1, 2))

1. Using ruff as a Python library · astral-sh/ruff · Discussion #8539 ↩