Getting Started with Flask: A Beginner’s Guide to Building Web Applications
Flask is a micro web framework written in Python that makes it easy to build web applications. Flask is popular for developing small to medium scale web applications as it is lightweight, easy to learn and provides a variety of built-in functionalities. In this article, we’ll give a beginner’s guide to getting started with Flask.
1. Install Flask
The first step in developing a Flask web application is to install Flask. Flask requires Python 2.7 or 3.3 or later. You can install Flask using pip, which is a Python package manager. To install Flask, open your terminal and type:
pip install Flask
This will install Flask and all its dependencies.
2. Create a Flask Application
After installing Flask, you can start building your web application. You can create a Flask application by creating a Python script and importing the Flask class. Once you import the Flask class, you can use it to create an instance of the Flask application.
from flask import Flask
app = Flask(__name__)
In the above code, we import the Flask class from the flask module and create an instance of Flask called app. The __name__ argument is a special Python variable that tells Flask the name of the current module.
3. Define Routes
Once you have created your Flask application, the next step is to define routes. A route is a URL that the application responds to. You can define routes using the @app.route decorator.
return ‘Hello, World!’
In the above code, we define a route using the @app.route decorator. The route / is the root URL of the application. When the user visits the root URL of the application, the function hello_world() is executed, and it returns the string ‘Hello, World!’.
4. Run the Application
After defining routes, you can run the Flask application. To run the Flask application, you need to add the following code to your Python script.
if __name__ == ‘__main__’:
The above code checks if the current module is the main module and then runs the Flask application. To start your Flask application, open your terminal and navigate to the directory where your Python script is located. Then run the following command:
This will start your Flask application, and it will be accessible at http://localhost:5000/.
5. Create Views
Once you have your Flask application up and running, the next step is to create views. Views contain the business logic of the application and are responsible for processing user input and returning responses.
@app.route(‘/login’, methods=[‘GET’, ‘POST’])
if request.method == ‘POST’:
username = request.form[‘username’] password = request.form[‘password’] if username == ‘admin’ and password == ‘secret’:
return ‘Logged In’
return ‘Invalid Credentials’
In the above code, we define a login view that handles both GET and POST requests. If the request method is POST, we get the username and password from the request.form object and check if they match the expected values. If the credentials are valid, we return the string ‘Logged In’, else we return ‘Invalid Credentials’.
If the request method is GET, we return an HTML form that lets the user enter their username and password.
6. Template Rendering
Flask provides a simple way to generate HTML pages using templates. Templates make it easy to separate the presentation logic from the business logic of the application.
from flask import render_template
return render_template(‘profile.html’, name=username)
In the above code, we define a profile view that takes a username as a parameter. We then use the render_template function to render the profile.html template. The render_template function takes the name of the template as the first argument and the variables that should be passed to the template as keyword arguments.
In this article, we gave a beginner’s guide to getting started with Flask. We covered the basics of installing Flask, creating a Flask application, defining routes, running the application, creating views, and template rendering. Flask is an excellent framework for building small to medium scale web applications. With Flask, you can quickly and easily build web applications with Python.
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