input: Write a function to create a virtual assistant using Python and Dialogflow to answer a basic set of questions. The function should initialize a Dialogflow session, continuously prompt the user for input, send the input to Dialogflow for processing, and then print the assistant's response. If the given input is empty then return an empty string.
  
  def virtual_assistant(project_id, session_id):
      import dialogflow_v2 as dialogflow
  
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, session_id)
  
      while True:
          text = input('User: ')
          if not text:
              return ''
          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') == ''
  
  # Sample interaction:
  # User: What is your name?
  # Assistant: My name is Assistant.
output: def virtual_assistant(project_id, session_id):
      import dialogflow_v2 as dialogflow
  
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, session_id)
  
      while True:
          text = input('User: ')
          if not text:
              return ''
          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)