input: Write a function to create a basic REST API using Python and Flask to list all the countries in the world. The function should initialize a Flask application, define a route for listing countries, read the countries from a JSON file, and return them as a JSON response. 
  
  def create_rest_api():
      import flask
      from flask import Flask, request, jsonify
      import json
  
      app = Flask(__name__)
  
      @app.route('/countries', methods=['GET'])
      def get_countries():
          with open('data.json', 'r') as f:
              countries = json.load(f)
          return jsonify(countries)
  
      if __name__ == '__main__':
          app.run()
  
  assert create_rest_api() is None
  assert '<Flask ' in str(create_rest_api())
output: 
  def create_rest_api():
      import flask
      from flask import Flask, request, jsonify
      import json
  
      app = Flask(__name__)
  
      @app.route('/countries', methods=['GET'])
      def get_countries():
          with open('data.json', 'r') as f:
              countries = json.load(f)
          return jsonify(countries)
  
      if __name__ == '__main__':
          app.run()
  