# Flask — The Python Micro Web Framework

> Flask is a lightweight WSGI web application framework for Python. Designed to make getting started quick and easy, with the ability to scale up to complex applications. The minimalist counterpart to Django, trusted by Netflix, LinkedIn, and Pinterest.

## Install

Save as a script file and run:

## Quick Use

```bash
pip install flask
```

```python
# app.py
from flask import Flask, jsonify, request

app = Flask(__name__)

assets = [
    {"id": 1, "repo": "react", "stars": 230000},
    {"id": 2, "repo": "vue",   "stars": 210000},
]

@app.get("/api/assets")
def list_assets():
    return jsonify(assets)

@app.post("/api/assets")
def create_asset():
    data = request.json
    asset = {"id": len(assets) + 1, **data}
    assets.append(asset)
    return jsonify(asset), 201

if __name__ == "__main__":
    app.run(debug=True)
```

```bash
python app.py
curl http://localhost:5000/api/assets
```

## Intro

Flask is a lightweight WSGI web application framework for Python. Created by Armin Ronacher in 2010 as part of the Pallets project. Flask is called a "micro framework" because it keeps the core simple but extensible — you choose your ORM, template engine, and tools. Trusted by Netflix, LinkedIn, Pinterest, Twilio, and the Python community at large.

- **Repo**: https://github.com/pallets/flask
- **Stars**: 71K+
- **Language**: Python
- **License**: BSD 3-Clause

## What Flask Does

- **Routing** — decorator-based URL rules
- **Templates** — Jinja2 template engine
- **Request/response** — Werkzeug WSGI utilities
- **Blueprints** — modular application components
- **Extensions** — Flask-SQLAlchemy, Flask-Login, Flask-CORS, Flask-Migrate, Flask-RESTful
- **CLI** — `flask run`, custom commands
- **Sessions** — cookie-based, configurable
- **Testing** — built-in test client
- **Context** — application and request context management
- **Signals** — Blinker-based event system

## Architecture

WSGI application. Request enters Werkzeug server, Flask routes it by matching URL rules (decorated functions). Request context is pushed per-request, providing access to `request`, `g`, `session` globals. Jinja2 renders HTML. Blueprints organize large apps into reusable modules.

## Self-Hosting

```bash
# Production (never use flask run in prod)
pip install gunicorn
gunicorn app:app --bind 0.0.0.0:8000 --workers 4

# Docker
FROM python:3.12-slim
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .
CMD ["gunicorn", "app:app", "--bind", "0.0.0.0:8000"]
```

## Key Features

- Minimal core (~1500 lines)
- Decorator-based routing
- Jinja2 templates
- Werkzeug request/response
- Blueprints for modularity
- Extensive extension ecosystem
- Built-in debugger
- Test client
- CLI via Click
- Flask 3.0+ requires Python 3.8+

## Comparison

| Framework | Type | Async | ORM |
|---|---|---|---|
| Flask | Micro | WSGI (sync) | Via extension |
| FastAPI | Async micro | ASGI | Via SQLAlchemy |
| Django | Full-stack | WSGI + ASGI | Built-in |
| Bottle | Micro | WSGI | None |
| Litestar | Async full | ASGI | Built-in |

## 常见问题 FAQ

**Q: Flask vs FastAPI？**
A: FastAPI 原生 async、自带 OpenAPI 文档和 Pydantic 验证，适合现代 API；Flask 更简单、生态更老牌、教程更多。新纯 API 项目推荐 FastAPI，全栈或已有项目用 Flask 很好。

**Q: Flask 支持 async 吗？**
A: Flask 2.0+ 支持 async views，但底层仍是 WSGI（在 threadpool 中跑 async）。真正的 async I/O 建议 FastAPI 或 Quart（Flask async 分支）。

**Q: 怎么组织大型项目？**
A: 用 Blueprints 按功能拆分模块。Application Factory 模式（`create_app()` 函数）支持不同环境配置。

## 来源与致谢 Sources

- Docs: https://flask.palletsprojects.com
- GitHub: https://github.com/pallets/flask
- License: BSD 3-Clause

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Source: https://tokrepo.com/en/workflows/65c0de18-3630-11f1-9bc6-00163e2b0d79
Author: Script Depot