How to define routes in Flask

Defining routes in Flask is a straightforward process. Here are the steps:

1. First, you need to import Flask from the flask module. This is done by adding the following line at the top of your Python file:

from flask import Flask

2. Next, you need to create an instance of the Flask class. This instance will be our WSGI application. You can create it as follows:

app = Flask(__name__)

3. Now, you can define a route using the route() decorator to tell Flask what URL should trigger our function. For example, if you want to define a route for the home page, you can do it as follows:

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

In this example, the URL '/' (which represents the home page) is bound to the home() function. So, whenever a user visits the home page of your application, the message "Hello, World!" will be displayed.

4. If you want to define routes with variable parts, you can add variable sections to the URL by marking sections with <variable_name>. For example:

@app.route('/user/<username>')
def show_user_profile(username):
    return 'User %s' % username

In this example, the URL '/user/John' will call the show_user_profile() function with the argument username set to 'John'.

5. Finally, if you want to make your application executable, you need to add the following lines at the end of your Python file:

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

This will run your application on the local development server.