old_contents: from flask import Flask, render_template
  from flask_bootstrap import Bootstrap
  
  
  app = Flask(__name__)
  Bootstrap(app)
  
  
  @app.route('/')
  def index():
      return render_template('index.html')
  
  
  if __name__ == '__main__':
      app.run()
  
new_contents: from flask import Flask, render_template
  from flask_bootstrap import Bootstrap
  from flask.ext.sqlalchemy import SQLAlchemy
  from sqlalchemy.orm.properties import ColumnProperty
  import os
  
  
  app = Flask(__name__)
  Bootstrap(app)
  app.config['SQLALCHEMY_DATABASE_URI'] = os.environ['DATABASE_URL']
  db = SQLAlchemy(app)
  
  
  class CaseInsensitiveComparator(ColumnProperty.Comparator):
      def __eq__(self, other):
          return db.func.lower(self.__clause_element__()) == db.func.lower(other)
  
  
  class Subscriber(db.Model):
      id = db.Column(db.Integer, primary_key=True)
      email = db.column_property(db.Column(db.String(256), unique=True, nullable=False), comparator_factory=CaseInsensitiveComparator)
  
  
  @app.route('/')
  def index():
      return render_template('index.html')
  
  
  if __name__ == '__main__':
      app.run()
  
subject: add database