input: Write a Python function to sum two numbers from URL parameters using Flask.
  assert get_sum('http://localhost:5000/get_sum?num1=4&num2=5')=='9'
  assert get_sum('http://localhost:5000/get_sum?num1=10&num2=20')=='30'
  assert get_sum('http://localhost:5000/get_sum?num1=-1&num2=1')=='0'
output: from flask import Flask, request
  
  app = Flask(__name__)
  
  @app.route('/get_sum', methods=['GET'])
  def get_sum():
      num1 = request.args.get('num1', type=int)
      num2 = request.args.get('num2', type=int)
      return str(num1 + num2)
  
  if __name__ == '__main__':
      app.run(debug=True)