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Learn from scratch the Flask installation guide to build a web application framework in Python

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Release： 2024-02-19 16:06:18

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Learn from scratch the Flask installation guide to build a web application framework in Python

Flask installation tutorial: Build a Python Web application framework from scratch, specific code examples are required

Introduction:
In modern Web development, building applications Frames play an important role. Python is a powerful and easy-to-learn programming language. There are many web development frameworks to choose from, and Flask is one of them. This article will introduce how to build a Flask application framework from scratch, with specific code examples.

1. Install Python
Flask is a Python-based web framework, so you need to install Python first. You can download the latest version of the Python installer from the official website (https://www.python.org/) and follow the prompts to install it.

2. Install Flask
After installing Python, you can install Flask. Run the following command on the command line:

pip install flask

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This will download and install the Flask package and its related dependencies from PyPI (Python Package Index).

3. Create a Flask application
After installing Flask, we can start creating a Flask application. First, create a file called app.py, which will serve as our main application file.

In app.py, enter the following code:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello_world():
    return "Hello, World!"

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

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In this code, we first imported the Flask module and created a file named ## The Flask application object of #app. Then, use the @app.route decorator to bind the URL path "/" to the hello_world function. Finally, use if __name__ == "__main__": to determine whether to execute in the main program mode, and call app.run() to start the Flask application.

4. Run the Flask application

To run the Flask application, you only need to execute the following command on the command line:

python app.py

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The Flask application will open a web server locally and listen to the default 5000 port. When you visit http://localhost:5000/ in the browser, you will see the simple string "Hello, World!".

5. Routing and View Function

In Flask applications, routing (Route) is used to map URL paths to view functions (View Functions). In the above example, we used the root path
"/" to bind the hello_world function.

Actually, we can create multiple routes to handle different URL paths. For example, we can create a

about route with a corresponding view function that returns information about our application.

Add the following code in

app.py:

@app.route("/about")
def about():
    return "This is a Flask application."

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After re-running the application, you can view "This is A Flask application." this string.

6. Templates and static files

In actual Web development, we usually need to use templates to dynamically generate HTML pages, and use static files to provide CSS, JavaScript and other static resources.

Flask has a built-in Jinja2 template engine, allowing us to use template files to render dynamic content. To use templates, we need to create a subdirectory called

templates within the application directory and create our template files in that directory.

For example, we can create a template file named

index.html:

<!DOCTYPE html>
<html>
<head>
    <title>Flask App</title>
</head>
<body>
    <h1>{{ message }}</h1>
</body>
</html>

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Introduce

render_template in app.py function, and modify the hello_world function to use template rendering:

from flask import Flask, render_template

app = Flask(__name__)

@app.route("/")
def hello_world():
    return render_template("index.html", message="Hello, Flask!")

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

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After re-running the application, you can see that the content displayed in the browser will be "Hello, Flask! ".

In order to use static files, we need to create a subdirectory named

static in the application directory and place the static files in it. Use the url_for function in the template file to generate the URL of the static file.

For example, we can introduce a static CSS file named

style.css in index.html:

<!DOCTYPE html>
<html>
<head>
    <title>Flask App</title>
    <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
</head>
<body>
    <h1>{{ message }}</h1>
</body>
</html>

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Create the style.css file in the static directory and add styles.

After re-running the application, you can see that the CSS style we defined will be applied to the page.

Summary:

This article introduces how to build a simple Flask application framework from scratch. We learned how to install Flask, create a Flask application, define routes and view functions, and use templates and static files. I hope this article will help you understand and learn Flask. I wish you success in web development!

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