input: Write a function to design a web server in Python using the Flask framework that serves a JSON object containing the current temperature for a city based on the city name given in the request. The function should include the Flask setup, the route for handling the request, and how to fetch and return the temperature data.
  
  assert get_temp(city="London")=={'temperature': 280.32}
  assert get_temp(city="Tokyo")=={'temperature': 290.15}
  assert get_temp(city="New York")=={'temperature': 278.01}
output: from flask import Flask, jsonify, request
  
  app = Flask(__name__)
  
  @app.route('/get_temp', methods=['GET'])
  def get_temp():
      city = request.args.get('city')
      temp_data = {
          "London": 280.32,
          "Tokyo": 290.15,
          "New York": 278.01
      }
      temperature = temp_data.get(city, None)
      if temperature is None:
          return jsonify({"error": "City not found"}), 404
      return jsonify({"temperature": temperature})