input: Write a function to create a virtual assistant using Python and Dialogflow to answer a basic set of questions. The function should continuously take user input and respond using Dialogflow's response. If the user inputs 'quit' or 'exit', the function should stop asking for input.
  import dialogflow_v2 as dialogflow
  import requests
  
  def virtual_assistant(project_id, session_id):
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, session_id)
  
      while True:
          text = input('User: ')
          if text.lower() in ['quit', 'exit']:
              break
          text_input = dialogflow.types.TextInput(text=text, language_code='en-US')
          query_input = dialogflow.types.QueryInput(text=text_input)
          response = session_client.detect_intent(session=session, query_input=query_input)
  
          print('Assistant:', response.query_result.fulfillment_text)
  
  assert virtual_assistant('project-id', 'session-id') == None
  assert virtual_assistant('another-project-id', 'another-session-id') == None
  assert virtual_assistant('invalid-project-id', 'invalid-session-id') == None
output: def virtual_assistant(project_id, session_id):
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, session_id)
  
      while True:
          text = input('User: ')
          if text.lower() in ['quit', 'exit']:
              break
          text_input = dialogflow.types.TextInput(text=text, language_code='en-US')
          query_input = dialogflow.types.QueryInput(text=text_input)
          response = session_client.detect_intent(session=session, query_input=query_input)
  
          print('Assistant:', response.query_result.fulfillment_text)