How to use the flask module for web development in Python 3.x

How to use the Flask module for Web development in Python 3.x

Introduction:
With the rapid development of the Internet, the demand for Web development is also increasing. To meet the needs of developers, many web development frameworks have emerged. Among them, Flask is a simple and practical web development framework. It is lightweight, flexible, and easy to expand. It is the first choice for many beginners and small and medium-sized projects.

This article will introduce you to how to use the Flask module in Python 3.x for web development, and provide some practical code examples.

Part One: Install Flask

Before we begin, first we need to install the Flask module. Flask can be installed from the command line using the following command:

pip install flask

Part 2: Create a simple Flask application

Next, we will create a simple Flask application. In this example, we will create a basic "Hello World" web page.

First, create a file named app.py in the code editor and enter the following code:

# 导入 Flask 模块
from flask import Flask

# 创建一个 Flask 应用实例
app = Flask(__name__)

# 创建一个路由，处理根目录访问
@app.route('/')
def hello_world():
    return 'Hello, world!'

# 运行应用
if __name__ == '__main__':
    app.run()

This code is very simple, it first imports The Flask module was installed, and then a Flask instance app was created. Next, use the decorator @app.route('/') to create a route that handles requests to access the root directory and returns a string "Hello, world!". Finally, the application is run via app.run().

After saving the code, execute the following command on the command line to run the application:

python app.py

If everything goes well, you will see output similar to the following:

 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

At this time You can enter http://127.0.0.1:5000/ in your browser and you will see the "Hello, world!" string.

Part 3: Routing and View Functions

In the above example, we created a simple route, processed the access request to the root directory, and returned a string. Now we'll cover more about routing and view functions.

Flask supports using different URL rules to define routes. Routes can be defined using the decorator @app.route. Here is an example:

# 创建一个路由，处理 /hello 路径的 GET 请求
@app.route('/hello')
def hello():
    return 'Hello, Flask!'

In this example, @app.route('/hello') defines a route that will handle GET requests accessing the /hello path, and Returns the string "Hello, Flask!".

View functions are functions that process requests and return responses. In the above example, hello() is a view function.

Part 4: Requests and Responses

In web development, requests and responses are very important concepts. Flask provides multiple ways to handle requests and responses.

Through the request object, you can access request-related information, such as path, parameters, form data, etc. Here is an example:

from flask import request

# 创建一个路由，处理 /search 路径的 GET 请求
@app.route('/search')
def search():
    keyword = request.args.get('keyword', '')  # 获取查询参数 keyword
    return 'You are searching for: ' + keyword

In this example, we use the request.args.get() method to get the value of the query parameter keyword and return a string.

To return a response, you can use the return statement or the make_response() function. Here is an example:

from flask import make_response

@app.route('/cookie')
def cookie():
    response = make_response('This is a cookie page.')
    response.set_cookie('username', 'john')  # 设置一个名为 username 的 cookie
    return response

In this example, we create a response object using the make_response() function and set it using the response.set_cookie() method A cookie named username is created.

Part 5: Template Engine

In actual Web development, we usually need to dynamically generate HTML pages. In order to easily implement this function, Flask provides a template engine.

When using a template engine, we can separate HTML code and dynamic content, making the code easier to maintain and develop. Here is an example using a template engine:

from flask import render_template

@app.route('/user/<username>')
def profile(username):
    return render_template('profile.html', name=username)

In this example, we use the render_template() function to render the template profile.html and pass the parameters ## The value of #username is passed to the template. In templates, you can use the {{ name }} syntax to output dynamic content.

This article introduces how to use the Flask module for web development in Python 3.x and provides some practical code examples. I hope readers can understand the basic usage of Flask through this article, and can further learn and explore more functions of the Flask framework. I wish you all success in web development!

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