input: Write a function to create a Python-based virtual assistant using Dialogflow that can answer a basic set of questions. The function should continuously prompt the user for input, send the input to Dialogflow for processing, and print the assistant's response. If the given project_id is invalid, the function should return an error message.
  import dialogflow_v2 as dialogflow
  import requests
  
  def virtual_assistant(project_id):
      try:
          session_client = dialogflow.SessionsClient()
          session = session_client.session_path(project_id, 'session-id')
      except Exception as e:
          return str(e)
  
      while True:
          text = input('User: ')
          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('valid-project-id')==None
  assert virtual_assistant('invalid-project-id').startswith('400')
output: 
  import dialogflow_v2 as dialogflow
  import requests
  
  def virtual_assistant(project_id):
      try:
          session_client = dialogflow.SessionsClient()
          session = session_client.session_path(project_id, 'session-id')
      except Exception as e:
          return str(e)
  
      while True:
          text = input('User: ')
          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)
  