old_contents: #!/usr/bin/env python
  
  from application import create_app
  from flask import render_template
  
  
  app = create_app('config_dev')
  
  @app.route('/')
  def home():
    return render_template('home.html')
  
  app.run()
  
new_contents: #!/usr/bin/env python
  
  import os
  from application import create_app
  from flask import render_template
  
  
  config_filename = 'config_' + (os.environ.get('env', 'prod')).lower()
  app = create_app(config_filename)
  
  @app.route('/')
  def home():
    return render_template('home.html')
  
  app.run()
  
subject: use config based on ENV