custom flask messages python

1{% with messages = get_flashed_messages(with_categories=true) %}
2    {% if messages %}
3        {% for category, message in messages %}
4            <div class="alert alert-{{ category }} alert-dismissible fade show" role="alert">
5                <span>{{ message }}</span>
6                <button type="button" class="close" data-dismiss="alert" aria-label="Close">
7                <span aria-hidden="true">×</span>
8                </button>
9            </div>
10        {% endfor %}
11    {% endif %}
12{% endwith %}
13

1flash(u'Invalid password provided', 'error')
2

1from flask import Flask, flash, redirect, render_template, \
2     request, url_for
3
4app = Flask(__name__)
5app.secret_key = b'_5#y2L"F4Q8z\n\xec]/'
6
7@app.route('/')
8def index():
9    return render_template('index.html')
10
11@app.route('/login', methods=['GET', 'POST'])
12def login():
13    error = None
14    if request.method == 'POST':
15        if request.form['username'] != 'admin' or \
16                request.form['password'] != 'secret':
17            error = 'Invalid credentials'
18        else:
19            flash('You were successfully logged in')
20            return redirect(url_for('index'))
21    return render_template('login.html', error=error)
22