Flask Academy · 课时

Hello World：您的第一个 Flask 应用

编写 app.py 并创建 Flask 应用对象

Hello World：您的第一个 Flask 应用 是 CoddyKit 上的免费 Flask Academy 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Flask Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flask Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Time to Build

You will now write your first Flask app and return a real response. It is just a few lines, and you already have everything installed. 🙌

Create app.py

Make a file named app.py in your project folder. This single file will hold your tiny first application.

Import Flask

Start by importing the Flask class. Everything you build hangs off the app object you are about to create.

from flask import Flask

Create the App Object

Instantiate Flask and pass __name__ so it knows where your app lives and can locate templates and static files.

app = Flask(__name__)

What name Does

The __name__ value tells Flask the import name of your module, which it uses to resolve resource paths correctly.

Add a Route

The @app.route decorator ties a URL path to the function right below it. Here the homepage path is just a slash.

@app.route('/')
def home():
    return 'Hello, World!'

The View Function

The function under a route is a view. Whatever string it returns becomes the body the browser displays.

Return a Response

Returning plain text is the simplest response. Flask wraps your string in a proper HTTP response automatically. 📨

The Main Guard

An if __name__ block lets you run the file directly. Inside it you call app.run to start the development server.

if __name__ == '__main__':
    app.run()

Run Your App

Launch it from the terminal. Flask prints a local address, usually on port 5000, where your app is now listening.

python app.py

See It in the Browser

Open http://127.0.0.1:5000 and your greeting appears. You just served your first web page with Python.

Quick Check

Quick check on wiring up your first app.

Recap

You imported Flask, built the app object, added a route and view, and ran it. Hello World is live in your browser. 🌍

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