Code Formatter

Code formatting best practices and quick references for Python, JavaScript, JSON, Markdown, and common languages with Prettier, Black, ESLint, and other formatters. Use when needing to format code, configure linters, or set up code style guidelines.

Code Formatter & Style Guide

Quick references for code formatting tools and style best practices.

---

🐍 Python Formatting

Black (Opinionated Formatter)

# Install
pip install black

# Format file
black file.py

# Format directory
black src/

# Check without modifying
black --check file.py

# Configuration (pyproject.toml)
[tool.black]
line-length = 88
target-version = ['py310']

isort (Import Sorting)

# Install
pip install isort

# Sort imports
isort file.py
isort src/

# Black-compatible config
[tool.isort]
profile = "black"

flake8 (Linting)

# Install
pip install flake8

# Lint
flake8 file.py
flake8 src/

# Config (setup.cfg)
[flake8]
max-line-length = 88
extend-ignore = E203, W503

ruff (Fast Linter & Formatter)

# Install
pip install ruff

# Lint
ruff check file.py

# Fix automatically
ruff check --fix file.py

# Format
ruff format file.py

---

💛 JavaScript/TypeScript Formatting

Prettier

# Install
npm install -D prettier

# Format
npx prettier --write file.js
npx prettier --write src/

# Check
npx prettier --check file.js

# Config (.prettierrc)
{
  "semi": true,
  "singleQuote": true,
  "tabWidth": 2,
  "trailingComma": "es5",
  "printWidth": 80
}

# Ignore (.prettierignore)
node_modules/
build/
dist/

ESLint

# Install
npm install -D eslint

# Initialize
npx eslint --init

# Lint
npx eslint file.js
npx eslint src/

# Fix
npx eslint --fix file.js

# Config (.eslintrc.js)
module.exports = {
  extends: ['eslint:recommended'],
  parserOptions: { ecmaVersion: 2022 },
  rules: {
    'no-unused-vars': 'warn',
    'no-console': 'warn'
  }
}

Format on Save (VS Code)

// settings.json
{
  "editor.defaultFormatter": "esbenp.prettier-vscode",
  "editor.formatOnSave": true,
  "[javascript]": {
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[python]": {
    "editor.defaultFormatter": "ms-python.black-formatter"
  }
}

---

📋 JSON Formatting

jq

# Pretty print JSON
jq '.' file.json

# Compact (one line)
jq -c '.' file.json

# Sort keys
jq -S '.' file.json

Prettier for JSON

npx prettier --write file.json
npx prettier --write *.json

Python json.tool

python3 -m json.tool file.json
python3 -m json.tool file.json --sort-keys

---

📝 Markdown Formatting

Prettier

npx prettier --write README.md
npx prettier --write docs/

markdownlint

# Install
npm install -D markdownlint-cli

# Lint
npx markdownlint README.md
npx markdownlint docs/

# Fix
npx markdownlint --fix README.md

Common Rules

• Line length: 80-120 chars
• ATX headers: # Header not Header =====
• Consistent list indentation (2 spaces)
• One blank line between sections
• Trailing whitespace removal

---

🔧 EditorConfig (Cross-Editor)

Create .editorconfig in project root:

root = true

[*]
charset = utf-8
end_of_line = lf
insert_final_newline = true
trim_trailing_whitespace = true
indent_style = space
indent_size = 2

[*.py]
indent_size = 4

[*.{json,yml,yaml}]
indent_size = 2

[*.md]
trim_trailing_whitespace = false

---

🚀 Quick Format Commands

Language	Tool	Command
Python	black	black file.py
Python	ruff	ruff format file.py
JS/TS	Prettier	npx prettier --write file.js
JSON	jq	jq '.' file.json
Markdown	Prettier	npx prettier --write README.md
Shell	shfmt	shfmt -w script.sh
Go	gofmt	gofmt -w file.go
Rust	rustfmt	rustfmt file.rs

---

💡 Best Practices

1. Commit config files: .prettierrc, .eslintrc, pyproject.toml, .editorconfig
2. Format on save: Set up your editor to auto-format
3. Pre-commit hooks: Use pre-commit or husky to enforce
4. Consistency: Pick one style and stick to it
5. CI checks: Run formatters/lint in CI pipeline

Pre-commit Setup (.pre-commit-config.yaml)

repos:
  - repo: https://github.com/psf/black
    rev: 23.12.1
    hooks:
      - id: black
  - repo: https://github.com/pycqa/isort
    rev: 5.13.2
    hooks:
      - id: isort
  - repo: https://github.com/pre-commit/mirrors-prettier
    rev: v4.0.0-alpha.8
    hooks:
      - id: prettier