Python Black Formatter

A developer-focused tool that formats Python code using Black rules, helping engineers deliver consistent code style for reviews and CI.

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684+

Total Calculations Run

< 15ms

Browser Execution Speed

100%

Client-Side Privacy

4.9 / 5.0

User Satisfaction

Worked Example & Common Values

Below is a sample worked calculation demonstrating how Python Black Formatter processes input data instantly inside your browser.

Sample Input Minified string: {"id":1,"status":"active","roles":["admin"]}

Computed Result

{
  "id": 1,
  "status": "active",
  "roles": [
    "admin"
  ]
}

Execution Mode Client-Side In-Browser JS

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About This Tool

The Python Black Formatter formats Python source code to Black's standardized style. It targets developers, code maintainers, and CI teams who require consistent formatting across a codebase. By applying a single, predictable set of rules, it reduces review friction and keeps diffs small.\n\nConceptually, inputs are tokenized and parsed where possible, then reflowed with line-length aware decisions. The tool emits a formatted string, preserving encoding and trailing newlines. It can read configuration from pyproject.toml or explicit options such as line_length and target_versions.\n\nUnique value stems from strict formatting focus, deterministic outputs, and an explicit changed flag with an optional diff. It supports Python version constraints to avoid introducing syntax changes, and it does not perform linting or bug fixes.\n\nCommon use cases include pre-commit formatting, CI checks, PR reviews, and onboarding new contributors. By automating style application, teams reduce manual edits, improve code consistency, and accelerate code reviews.

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How to Use

Provide inputs: supply source_code and optional settings (line_length, target_versions, skip_string_normalization).
Choose method: apply formatting using the specified options; outputs will include formatted_code and a diff if requested.
Run calculation: format code and compare with the input to determine changes.
Review outputs: inspect formatted_code and diff; run a quick syntax check if needed.
Integrate: add to CI or pre-commit to enforce style; save results for auditing.

Frequently Asked Questions

Find Quick Answers

What language does this tool format?

It formats Python source code only, applying Black-style rules to enforce a consistent code appearance. It does not format non-Python languages or perform non-formatting lint checks.

What if the input code cannot be parsed?

If the Python code contains syntax errors, the formatter raises a detailed error that includes the line number and issue. No formatted output is returned until the input is syntactically valid.

Can I customize line length or other options?

Yes. You can set line_length and target_versions, with sensible defaults. You may also toggle string normalization and rely on pyproject.toml for configuration to control behavior across the project.

Does it preserve trailing newlines or encoding?

The formatter preserves the input's trailing newline status and uses UTF-8 encoding by default. Indentation and whitespace decisions follow Black-style rules to ensure uniform formatting.

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