Flask Basics for Beginner Developers

Flask is a very lightweight and flexible python web framework, designed to help developers to build web applications quickly and efficiently.

Framework?

A Framework is a software structure designed to simplify the process of developing web applications. It provides a collection of pre-written code, tools, and libraries that help developers in creating websites, web services and different APIs more efficiently.

Some of the major advantages of Flask

Simplicity

Flask is straightforward and has very intuitive syntax, A new beginner developer can use it with ease even with minimal experience of python.
Modularity

Flask’s modular design means we can integrate only the components we need, avoiding excessive codebases. Developers can start with the very basics and add extentions (like database or authentication) as the project grows.
Extensibility

Flask has a diverse extensions such as Flask-SQLAlchemy (for databases), Flask-WTF (for forms), Flask-RESTful (for APIs).

Defination and History

Flask is considered as a “micro-framework” .Unlike larger frameworks like Django, Flask does not come with built-in tools like an ORM(Object-Relational Mapper) or authentication system. Instead, it gives developers the freedom to chose and integrate what they really need.

micro-framework?

Micro-framework, A framework that keeps the core simple and lets developers add features using external libraries or extensions.

Flask was first released on 2010, It has very simple philosophy i.e, “Simple is better than complex”.

Flask is built on top of two libraries

Jinja2: A templating engine for dynamic HTML generation
Werkzeug: A library for handling HTTP requests.

Setting Up Your Flask Environment

Setting up flask environment is an easy-peasy task. Tools needed: Python, pip, virtual environment.

Installation of Flask

pip install flask

file structure for your project

my_flask_app/
├── app.py
├── static/
├── templates/
└── venv/

Let’s try to build our first Flask App

A simplest example, initiate the app

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
    return "Namaste! everyone"

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

lets try to understand each component

from flask import Flask
this imports the Flask class from the Flask library, which is the foundation for building a Flask application.
app = Flask(__name__)
Flask is a class used to create a Flask application instance.
The __name__ variable is a special Python variable that represents the name fo the current module(the file being executed).
Flask uses this name to determine the location of the application (useful for finding resources like templates and static files).

application instance
In Flask, the application instance is the central object that represents your web application. It's created by instantiating the Flask class, and it serves as the entry point for defining your app's behavior, such as handling requests, routing, and configuring settings.
@app.route(“/”)
this is a decorator that maps the URL path / (the root of your website, like http://localhost:5000/) to the home function.
def home():
this defines a Python function called home.
return “Namaste! everyone”:
this specifies the response that will be sent back to the user’s browser when they visit the / route. In this case, the browser will display Namate! everyone
if name == “__main__”:
this ensures that the code inside this block only runs when the script is executed directly(e.g. python app.py) and not when it’s imported as a module in another script.
app.run(debug=True)
this starts the Flask development server to handle incoming requests. debug=True enables debug mode, which automatically restarts the server when code changes and provides detailed error messages for easier debugging.

Adding Templates and Static files

<html>
<head>
    <title>Flask App</title>
</head>
<body>
    <h1>Welcome to Flask!</h1>
</body>
</html>

Templates

Templates are crucial part of web development because they enable the generation of dynamic content for your application. Instead of writing static HTML pages for every scenario, templates allow you to insert variables and loop through data, making your web pages interactive and adaptable to user input or backend data.

Jinja2

Jinja2 is the default templating engine used in Flask. It allows you to embed Python-like expressions directly into your HTML files. With Jinja2, you can use variable, loops, conditional statements and even custom filters to render dynamic content.

Key features in Jinja2:

{{ variable }}: inserts dynamic content (e.g., {{ username }}.
{% for …%}: loops through data
{% if…%}: Adds conditonal logic

Handling Forms and routes

from flask import request

@app.route("/submit, methods=["POST"])
def submit():
    name = request.form.get("name")
return f"Hello, {name}!"

methods=[“POST”]: By default, Flask routes handle GET requests. The methods parameter specifies which HTTP methods are allowed for the route. Here, POST is specifies, meaning this route will only respond to POST request
def submit(): This is the Python function that will execute when the /submit route is accessed via a POST request.
name = request.form.get(“name”)
request Object: the request object in Flask provides access to the data sent by the client
request.form : the form attribute contains the form data sent in the body of a POST request. It’s a dictionary-like object.
.get(“name”): this retrieves the value associated with the key “name” from the form data. If no value exists for “name”, it returns None by default.

Connecting to a Database(Optional):
You can connect Database like SQLite with Flask-SQLAlchemy for storing data.
Now you can run your application.
if you have initiated your app in the app.py file, then you can run your application by runnig the script python app.py in the terminal.

Now that you have got the basics of Flask, it’s time to create your own project! Start small- perhaps a personal homepage or a basic app that displays quotes.
Don’t be afraid to make mistakes, every error is a step closer to mastery. Happy coding!

Resources for further Learning:
Official Flask documentation

An Introduction to beginner friendly Flask for beginner developers

Some of the major advantages of Flask

Defination and History

Setting Up Your Flask Environment

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NIRAJ

NIRAJ