old_contents: from flask_assets import Bundle, Environment
  from flask import current_app
  
  bundles = {
    'root_js': Bundle(
      'js/lib/jquery-2.1.1.min.js',
      'js/app.js',
      output='dist/bundle.js'),
    
    'root_css': Bundle(
      'css/lib/reset.css',
      'css/common.css',
      'css/app.css',
      output='dist/styles.css')
  }
  
new_contents: from flask_assets import Bundle, Environment
  from flask import current_app as app
  
  bundles = {
    'root_js': Bundle(
      'js/lib/jquery-2.1.1.min.js',
      'js/app.js',
      output='dist/bundle.js'),
    
    'root_css': Bundle(
      'css/lib/reset.css',
      'css/common.css',
      'css/app.css',
      output='dist/styles.css')
  }
  
  assets = Environment(app)
  assets.register(bundles)
  
subject: Update assets.py