input: Write a python function to create a GUI window with two buttons, one to print "Hello World!" and another to exit the application.
  assert type(create_gui()) == type(None)
output: def create_gui():
      import tkinter as tk
  
      def print_hello():
          print("Hello World!")
  
      def exit_app():
          root.destroy()
  
      root = tk.Tk()
      root.title("Simple GUI")
  
      hello_button = tk.Button(root, text="Print Hello", command=print_hello)
      hello_button.pack()
  
      exit_button = tk.Button(root, text="Exit", command=exit_app)
      exit_button.pack()
  
      root.mainloop()