input: 
  from flask import Flask
  import datetime
  
  app = Flask(__name__)
  
  @app.route('/datetime')
  def get_datetime():
      """ Create a web API using Flask that returns the current date and time in the 
      format "YYYY-MM-DD HH:MM:SS" when accessed through the route '/datetime'.
      
      Example:
      When accessing '/datetime' through a web browser or HTTP client, the API should 
      return something like '2023-10-05 14:30:45'.
      """
      return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
  
  if __name__ == '__main__':
      app.run()
  
output:     
      return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
  