old_contents: from flask import render_template
  from . import main
  from flask_login import current_user
  
  @main.route('/')
  def index():
  	return render_template('index.html', current_user=current_user) 
new_contents: from flask import render_template, abort 
  from . import main
  from flask_login import current_user
  from ..models import User 
  
  @main.route('/')
  def index():
  	return render_template('index.html', current_user=current_user) 
  
  @main.route('/user/<username>')
  def user(username):
  	user = User.query.filter_by(username=username).first()
  	if user is None:
  		abort(404)
  	return render_template('user.html', user=user)
subject: add a user profile route