Handling forms is a critical part of most web applications — whether it’s a login form, a contact form, or a comment box. In this post, we’ll break down how to properly handle HTML forms in Flask, including:
- Displaying a form with HTML
- Handling
POSTandGETrequests - Validating form input
- Providing user feedback
Basic Flask Setup
# app.py
from flask import Flask, render_template, request, redirect, url_for, flash
app = Flask(__name__)
app.secret_key = 'supersecretkey' # Needed for flashing messagesStep 1: Create an HTML Form
templates/form.html
<!DOCTYPE html>
<html>
<head>
<title>Simple Form</title>
</head>
<body>
<h2>Contact Us</h2>
<form method="POST" action="/submit">
<label>Name:</label><br>
<input type="text" name="name" required><br><br>
<label>Message:</label><br>
<textarea name="message" required></textarea><br><br>
<button type="submit">Send</button>
</form>
{% with messages = get_flashed_messages() %}
{% if messages %}
<ul>
{% for msg in messages %}
<li>{{ msg }}</li>
{% endfor %}
</ul>
{% endif %}
{% endwith %}
</body>
</html>Step 2: Handle Form Submission in Flask
@app.route('/')
def home():
return render_template('form.html')
@app.route('/submit', methods=['POST'])
def submit():
name = request.form.get('name')
message = request.form.get('message')
if not name or not message:
flash('All fields are required!')
return redirect(url_for('home'))
# Here you would typically save to a database
flash(f"Thanks, {name}! Your message was received.")
return redirect(url_for('home'))What’s Happening Here?
request.form.get('name'): Safely gets the submitted form dataflash(): Stores a temporary message shown after redirectredirect()+url_for(): Prevents form resubmission on refresh (Post/Redirect/Get pattern)
Step 3: Test It Out
Run your app:
flask runOpen http://localhost:5000, fill out the form, and submit. You’ll see a flash message on success!
Bonus: Adding Simple Validation
You can manually validate fields before using them:
if len(name) < 3:
flash("Name must be at least 3 characters long.")
return redirect(url_for('home'))For more advanced forms (e.g. email, password fields, CSRF protection), look into Flask-WTF, which adds built-in form validation and helpers.