0from flask import Flask, flash, redirect, render_template, request, url_for app = Flask(__name__) app.secret_key = 'your_secret_key' @app.route('/submit', methods=['POST']) def submit(): flash('Form submitted successfully!') return redirect(url_for('index'))
| Step | Action | Flash Message Set | Redirect or Render | Message Displayed |
|---|---|---|---|---|
| 1 | User submits form | No | No | No |
| 2 | Server receives POST /submit | No | No | No |
| 3 | flash('Form submitted successfully!') called | Yes: 'Form submitted successfully!' | No | No |
| 4 | return redirect(url_for('index')) | Yes | Redirect to /index | No |
| 5 | User browser requests /index | No | No | No |
| 6 | Server renders index template | No | Render index.html | Yes: 'Form submitted successfully!' shown |
| 7 | Flash message removed after display | No | No | No |
| Variable | Start | After Step 3 | After Step 6 | Final |
|---|---|---|---|---|
| flash_messages | [] | ['Form submitted successfully!'] | ['Form submitted successfully!'] | [] |
Flash messages in Flask:
- Use flash('message') to store feedback
- Redirect to another route to show message
- In template, use get_flashed_messages() to display
- Messages show once then clear
- Helps inform users about actions like form submissionflash() 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.