Python Web Development with Flask — Flash Messages

Photo by Fabio Ballasina on Unsplash

Flask is a simple web framework written in Python.

In this article, we’ll look at how to develop simple Python web apps with Flask.

Message Flashing

We can send messages to a template that can be accessed with the next request.

For example, we can write:

app.py

from flask import Flask, render_template, redirect, url_for, flash, request
app = Flask(__name__)
app.secret_key = b'secret'
@app.route('/')
def index():
    return render_template('index.html')
@app.route('/login', methods=['GET', 'POST'])
def login():
    error = None
    if request.method == 'POST':
        flash('You were successfully logged in')
        return redirect(url_for('index'))
    return render_template('login.html', error=error)

templates/login.html

{% block body %}
  <h1>Login</h1>
  {% if error %}
    <p class=error><strong>Error:</strong> {{ error }}
  {% endif %}
  <form method=post>
    <dl>
      <dt>Username:
      <dd><input type=text name=username value="{{
          request.form.username }}">
      <dt>Password:
      <dd><input type=password name=password>
    </dl>
    <p><input type=submit value=Login>
  </form>
{% endblock %}