input: Write a function to create a virtual assistant using Python and Dialogflow to answer a basic set of questions. The function should take no input and should continuously prompt the user for input, sending the input to Dialogflow, and then printing the response from Dialogflow.
  assert create_virtual_assistant()==None
  assert create_virtual_assistant()==None
output: def create_virtual_assistant():
      import dialogflow_v2 as dialogflow
      import os
  
      os.environ["GOOGLE_APPLICATION_CREDENTIALS"] = "path_to_your_credentials_file.json"
  
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path("your-project-id", "unique-session-id")
  
      while True:
          user_input = input("You: ")
          text_input = dialogflow.types.TextInput(text=user_input, 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)