Flask Academy · レッスン

Hello World：初めてのFlaskアプリ

app.pyを書き、Flaskアプリケーションオブジェクトを作成します

「Hello World：初めてのFlaskアプリ」はCoddyKit上の無料Flask Academyレッスンです。これはレッスン3/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはFlask Academy学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Flask Academyコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

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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