ScriptsApr 12, 2026·1 min read

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.

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Quick Use

Use it first, then decide how deep to go

This block should tell both the user and the agent what to copy, install, and apply first.

pip install flask
# 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)
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.

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

# 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

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