Python Formatter

What this tool does

The Python formatter rewrites Python code in the widely used Black style: consistent indentation, spaces around operators, double quotes, two blank lines between top-level definitions and long lines wrapped at sensible places.

Under the hood it runs the formatter from Ruff, the fast Python linter and formatter written in Rust, compiled to WebAssembly. Ruff’s output matches Black almost line for line, so code formatted here will not be reformatted again by your project’s pre-commit hook.

How to use it

1. Paste Python code, or open a .py file.
2. The formatted code appears on the right as you type.
3. Adjust the options if your project uses a different style:
   • Indent: 4 spaces is PEP 8 and the default; 2 spaces and tabs are available.
   • Line width: 88 is Black’s default, 79 is PEP 8’s limit, and 100 or 120 suit wider screens.
   • Quotes: double, single, or keep the quotes each string already uses.
   • Respect trailing commas: keep collections that end with a comma expanded.
4. Copy or download the result.

When the code cannot be parsed, the error message shows where the parser stopped, such as Expected `,`, found `=` on line 4, and you can jump to that line.

Example

The sample is a small module written carelessly: imports on one line with no spaces, a dataclass with a space before the colon, a method indented with two spaces and a one-line if statement. After formatting, every block uses four-space indentation, the if body moves onto its own line, operators get spaces, single quotes become double quotes and blank lines are added between the class and functions. The list that ended with a trailing comma is expanded with one dictionary per line.

What the formatter does not do

Formatting only changes layout. It does not sort imports, remove unused variables or rename anything; those are linter jobs (ruff check --fix handles them). Comments and docstrings are kept, and the formatter refuses to change code it cannot parse rather than guessing.

Tips

• Use the same line width as your project’s pyproject.toml so the result matches your CI.
• Formatting a snippet before posting it in a question or review makes it much easier to read.
• If the code came from a notebook or a chat and has mixed tabs and spaces, the formatter normalises it in one step.