Python Development

Project Setup

Create project with uv

uv init my-project cd my-project

Add dependencies

uv add litestar uv add --dev pytest ruff mypy

pyproject.toml

[project] name = "my-project" version = "0.1.0" requires-python = ">=3.13" dependencies = ["litestar>=2.0"]

[tool.ruff] line-length = 88 target-version = "py313"

[tool.mypy] strict = true python_version = "3.13"

Type Hints

from typing import TypeVar, Generic from collections.abc import Sequence

T = TypeVar('T')

class Repository(Generic[T]): async def find_by_id(self, id: str) -> T | None: ...

async def save(self, entity: T) -> T:
    ...

def process_items(items: Sequence[str]) -> list[str]: return [item.upper() for item in items]

Async Patterns

import asyncio from collections.abc import AsyncIterator

async def fetch_all(urls: list[str]) -> list[Response]: async with aiohttp.ClientSession() as session: tasks = [fetch_one(session, url) for url in urls] return await asyncio.gather(*tasks)

async def stream_data() -> AsyncIterator[bytes]: async with aiofiles.open('large.csv', 'rb') as f: async for chunk in f: yield chunk

Error Handling

from dataclasses import dataclass from typing import TypeVar, Generic

T = TypeVar('T') E = TypeVar('E')

@dataclass class Ok(Generic[T]): value: T

@dataclass class Err(Generic[E]): error: E

Result = Ok[T] | Err[E]

def divide(a: int, b: int) -> Result[float, str]: if b == 0: return Err("Division by zero") return Ok(a / b)

Testing with pytest

import pytest from unittest.mock import AsyncMock

@pytest.mark.asyncio async def test_create_user(): repo = AsyncMock() service = UserService(repo)

user = await service.create("test@example.com")

assert user.email == "test@example.com"
repo.save.assert_called_once()

@pytest.fixture def mock_database(): with patch('app.database') as mock: yield mock

Tooling

Ruff (linting + formatting)

ruff check --fix . ruff format .

MyPy (type checking)

mypy --strict .

pytest

pytest -v --cov=src