input: Write a python function to create a chatbot that responds to predefined inputs.
  assert chatbot.respond('hello') == 'Hi there!'
  assert chatbot.respond('how are you?') == 'I am doing well. How about you?'
  assert chatbot.respond('goodbye') == 'Goodbye, have a nice day!'
  assert chatbot.respond('unknown input') == None
output: def chatbot():
      responses = {
          'hello': 'Hi there!',
          'how are you?': 'I am doing well. How about you?',
          'goodbye': 'Goodbye, have a nice day!'
      }
      
      def respond(input_text):
          return responses.get(input_text, None)
      
      return type('Chatbot', (object,), {'respond': staticmethod(respond)})()
  
  chatbot = chatbot()