0Flash messages show quick notes to users after actions, like "Success" or "Error". They help users know what happened.
from flask import flash flash('Your message here', 'category')
The flash() function stores a message for the next page load.
The optional category helps style messages differently, like 'error' or 'success'.
flash('Login successful', 'success')
flash('Invalid password', 'error')
flash('Welcome back!')This Flask app shows a form to enter a username. When submitted, it flashes a success message if a username is entered or an error if empty. The messages appear on the page with colors.
from flask import Flask, render_template_string, request, redirect, url_for, flash, get_flashed_messages app = Flask(__name__) app.secret_key = 'secret123' # Needed for flashing messages @app.route('/', methods=['GET', 'POST']) def index(): if request.method == 'POST': username = request.form.get('username', '') if username: flash(f'Welcome, {username}!', 'success') return redirect(url_for('index')) else: flash('Please enter a username.', 'error') return redirect(url_for('index')) messages = get_flashed_messages(with_categories=True) return render_template_string(''' <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Flash Messages Demo</title> <style> body { font-family: Arial, sans-serif; padding: 2rem; } .flash { padding: 1rem; margin-bottom: 1rem; border-radius: 0.5rem; } .success { background-color: #d4edda; color: #155724; } .error { background-color: #f8d7da; color: #721c24; } </style> </head> <body> <h1>Enter your username</h1> <form method="POST"> <input type="text" name="username" aria-label="Username" required> <button type="submit">Submit</button> </form> {% for category, message in messages %} <div class="flash {{ category }}" role="alert">{{ message }}</div> {% endfor %} </body> </html> ''', messages=messages) if __name__ == '__main__': app.run(debug=True)
Always set app.secret_key to enable flashing.
Use get_flashed_messages(with_categories=True) to get messages with their categories for styling.
Flash messages last only for the next request, so they disappear after showing once.
Flash messages give quick feedback to users after actions.
Use flash() to store messages and display them in templates.
Categories help style messages differently, like success or error.
flash() in a Flask application?flash() doesflash() function stores these messages to be displayed once, then removed.flash in a Flask app?flash are imported directly from the flask package using from flask import flash.flash('Message') is the correct way to flash a message.from flask import Flask, flash, render_template_string, get_flashed_messages
app = Flask(__name__)
app.secret_key = 'secret'
@app.route('/')
def index():
flash('Welcome back!', 'info')
messages = get_flashed_messages(with_categories=True)
return render_template_string('''
{% for category, message in messages %}
<div class="{{ category }}">{{ message }}</div>
{% endfor %}
''', messages=messages)get_flashed_messages(with_categories=True) returns a list of (category, message) tuples.from flask import Flask, flash
app = Flask(__name__)
@app.route('/')
def index():
flash('Hello user!')
return 'Done'app.secret_key to be set.app.secret_key, so flashing will not work properly and may raise an error.flash('message', 'category') -- category as the second positional argument.get_flashed_messages(with_categories=True) directly in the template to unpack (category, message) and apply class="{{ category }}" for distinct styles.type='success' raises TypeError; retrieving without with_categories=True returns strings causing unpack error in for category, msg in messages.{{ msg }}
\n{% endfor %} [OK]Pass the test and this pattern moves unknown strong while earning +1 Grip toward your certificate.