input: Write a function to create a virtual assistant using Python and Dialogflow to answer a basic set of questions. The function should interact with Dialogflow, take user input, and print the assistant's response. If the project ID or session ID is not provided, the function should return an error message.
  import dialogflow_v2 as dialogflow
  import requests
  
  def create_virtual_assistant(project_id, session_id):
      if not project_id or not session_id:
          return "Error: Project ID or Session ID not provided."
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, session_id)
      
      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 create_virtual_assistant('project-id', 'session-id') is None
  assert create_virtual_assistant('', 'session-id') == "Error: Project ID or Session ID not provided."
  assert create_virtual_assistant('project-id', '') == "Error: Project ID or Session ID not provided."
  assert create_virtual_assistant('', '') == "Error: Project ID or Session ID not provided."
output: def create_virtual_assistant(project_id, session_id):
      if not project_id or not session_id:
          return "Error: Project ID or Session ID not provided."
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, session_id)
      
      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)