pip install flask-bootstrap

{% extends "bootstrap/base.html" %}

{% block title %}Flask{% endblock %}

{% block navbar %}
  <div class="navbar navbar-inverse" role="navigation">
    <div class="container">
      <div class="navbar-header">
        <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
          <span class="sr-only">Toggle navigation</span><span class="icon-bar"></span>
          <span class="icon-bar"></span><span class="icon-bar"></span>
        </button>
        <a class="navbar-brand" href="/" rel="external nofollow" rel="external nofollow" >Flask</a>
      </div>
      <div class="navbar-collapse collapse">
        <ul class="nav navbar-nav">
          <li><a href="/" rel="external nofollow" rel="external nofollow" >Home</a></li>
        </ul>
      </div>
    </div>
  </div>
{% endblock %}

{% block content %}
  <div class="container">
    <div class="page-header">
      <h1>Hello, {{ name }}</h1>
    </div>
  </div>
{% endblock %}

from flask import Flask, render_template
from flask_bootstrap import Bootstrap

app = Flask(__name__)
bootstrap = Bootstrap(app)


@app.route('/user/<name>')
def user(name):
  return render_template('user.html', name=name)


if __name__ == '__main__':
  app.run()