Code Style & Formatting

Objectives

•Configure and run code formatters (Prettier, Black, Ruff)
•Set up linters (ESLint, Ruff, mypy)
•Fix style violations automatically
•Establish pre-commit hooks for consistency

Python Style

Tools

•Ruff: Fast linter + formatter (replaces Black, isort, flake8)
•mypy: Static type checker
•pyproject.toml: Configuration file

Configuration

toml

# pyproject.toml
[tool.ruff]
line-length = 100
target-version = "py310"

[tool.ruff.lint]
select = [
    "E",   # pycodestyle errors
    "W",   # pycodestyle warnings
    "F",   # pyflakes
    "I",   # isort
    "N",   # pep8-naming
    "UP",  # pyupgrade
]
ignore = ["E501"]  # Line too long (handled by formatter)

[tool.mypy]
python_version = "3.10"
strict = true
warn_return_any = true
warn_unused_configs = true

Commands

bash

# Format code
ruff format .

# Check and fix linting issues
ruff check --fix .

# Type check
mypy src/

# Run all checks
ruff format . && ruff check --fix . && mypy src/

TypeScript/JavaScript Style

Tools

•Prettier: Code formatter
•ESLint: Linter
•TypeScript: Type checker

Configuration

javascript

// eslint.config.js
export default [
  {
    files: ["**/*.{ts,tsx}"],
    rules: {
      "no-console": "warn",
      "no-unused-vars": "error",
      "@typescript-eslint/no-explicit-any": "error",
      "react-hooks/rules-of-hooks": "error",
    },
  },
];

json

// .prettierrc
{
  "semi": true,
  "singleQuote": false,
  "tabWidth": 2,
  "trailingComma": "es5",
  "printWidth": 100
}

Commands

bash

# Format code
npm run format
# or
npx prettier --write "src/**/*.{ts,tsx}"

# Lint and fix
npm run lint
# or
npx eslint --fix "src/**/*.{ts,tsx}"

# Type check
npx tsc --noEmit

Style Rules

Formatting

•Line length: 100 characters (Python and TypeScript)
•Indentation: 4 spaces (Python), 2 spaces (TypeScript)
•Quotes: Double quotes (TypeScript), either (Python, but consistent)
•Trailing commas: Yes (for multi-line)
•Semicolons: Yes (TypeScript)

Naming (enforced by linters)

python

# Python
class UserService:           # PascalCase
    MAX_RETRIES = 3         # UPPER_SNAKE_CASE

    def get_user(self):     # snake_case
        user_id = 123       # snake_case
        return user_id

typescript

// TypeScript
class UserService {
  // PascalCase
  private readonly maxRetries = 3; // camelCase

  getUser(): User {
    // camelCase
    const userId = 123; // camelCase
    return user;
  }
}

Imports

python

# Python: Sorted by Ruff (isort)
import os
import sys
from pathlib import Path

import requests
from fastapi import FastAPI

from src.core.models import User
from src.services.auth import AuthService

typescript

// TypeScript: Sorted by ESLint
import { useState, useEffect } from "react";
import type { User } from "@/types";

import { Button } from "@/components/ui/button";
import { authService } from "@/services/auth";

Type Annotations

Python

python

# Always annotate function signatures
def get_user(user_id: int) -> User | None:
    """Get user by ID."""
    return db.query(User).get(user_id)

# Use modern syntax (Python 3.10+)
def process_items(items: list[str]) -> dict[str, int]:
    return {item: len(item) for item in items}

TypeScript

typescript

// Prefer explicit types for public APIs
function getUser(userId: number): User | null {
  return db.users.find(userId);
}

// Use type inference for locals
const users = await fetchUsers(); // Type inferred

Documentation

Python Docstrings

python

def calculate_score(
    user_id: int,
    weights: dict[str, float],
    normalize: bool = True
) -> float:
    """Calculate weighted score for user.

    Args:
        user_id: User identifier
        weights: Feature weights mapping
        normalize: Whether to normalize to [0, 1]

    Returns:
        Calculated score

    Raises:
        ValueError: If user not found
    """
    pass

TypeScript JSDoc

typescript

/**
 * Calculate weighted score for user
 *
 * @param userId - User identifier
 * @param weights - Feature weights mapping
 * @param normalize - Whether to normalize to [0, 1]
 * @returns Calculated score
 * @throws {Error} If user not found
 */
function calculateScore(
  userId: number,
  weights: Record<string, number>,
  normalize = true,
): number {
  // ...
}

Pre-commit Hooks

Python (using pre-commit)

yaml

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.1.9
    hooks:
      - id: ruff
        args: [--fix]
      - id: ruff-format

  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.8.0
    hooks:
      - id: mypy
        additional_dependencies: [types-requests]

Install: pre-commit install

TypeScript (using husky + lint-staged)

json

// package.json
{
  "lint-staged": {
    "*.{ts,tsx}": ["eslint --fix", "prettier --write"]
  }
}

Install: npx husky install && npx husky add .husky/pre-commit "npx lint-staged"

Auto-fix Workflow

When style issues are found:

•

Run formatter first (fixes most issues)

bash

ruff format .              # Python
prettier --write .         # TypeScript

•

Run linter with auto-fix

bash

ruff check --fix .         # Python
eslint --fix .             # TypeScript

•

Check remaining issues

bash

ruff check .               # Python
eslint .                   # TypeScript

•

Type check

bash

mypy src/                  # Python
tsc --noEmit               # TypeScript

Common Issues

Python

•Import order: Let Ruff handle it automatically
•Line too long: Use formatter, or add # noqa: E501 if necessary
•Type errors: Add type annotations or use # type: ignore[error-code]

TypeScript

•Any types: Replace with proper types or use unknown
•Unused vars: Remove or prefix with _ if intentionally unused
•Missing return types: Add explicit return type annotations

IDE Integration

VS Code

json

// .vscode/settings.json
{
  "editor.formatOnSave": true,
  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": "explicit"
  },
  "[python]": {
    "editor.defaultFormatter": "charliermarsh.ruff"
  },
  "[typescript]": {
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  }
}

Validation Checklist

Before committing:

• Code is formatted (Prettier/Ruff)
• No linting errors (ESLint/Ruff)
• Type checks pass (TypeScript/mypy)
• All imports are sorted
• No unused variables or imports
• Functions have type annotations
• Public APIs have documentation

Project-Specific Rules

Check for project overrides in:

•pyproject.toml (Python)
•eslint.config.js (TypeScript)
•.prettierrc (TypeScript)
•.vscode/settings.json (IDE settings)

Load these files first to understand project conventions.