Forms and Requests

Web applications become interactive when users can send data to the server.

Forms allow users to submit data, and Flask processes that data through requests.

What are Forms?

Forms are HTML elements used to collect user input.

Example:

id="html-form"

<form method="POST"> <input type="text" name="username"> <button type="submit">Submit</button> </form>

Handling Form Data in Flask

Flask provides a request object to access incoming data.

Example:

id="handle-form"

from flask import Flask, request app = Flask(__name__) @app.route("/submit", methods=["GET", "POST"]) def submit(): if request.method == "POST": username = request.form.get("username") return f"Hello, {username}" return "Submit a form"

How It Works

The user fills out a form
The browser sends a POST request
Flask receives the request
Data is extracted from the request
A response is returned

Forms Flow Diagram

GET vs POST

Forms can use different HTTP methods.

GET

Data is sent in the URL
Used for retrieving data

POST

Data is sent in the request body
Used for submitting data

Accessing Form Data

Flask provides different ways to access data:

request.form → form data
request.args → query parameters
request.json → JSON data

Why This Matters

Handling user input is essential for:

Login systems
Registration forms
Search functionality
User interactions

Challenge

Create a form that sends data to your server.

What to do

Create an HTML form with:
- A text input for name
- A submit button
Set the form method to POST
Create a Flask route that handles both GET and POST
Inside the route:
- Check if the request method is POST
- Get the name using request.form.get()
Return a message like:
“Hello, John”

What you should test

Enter a name in the form
Submit it
The page should display your name

Summary

Forms collect user input
Flask processes form data using the request object
GET and POST methods handle different types of requests

In the next lesson, you’ll learn how to return JSON responses and build APIs.