input: 
  from flask import Flask
  import datetime
  
  app = Flask(__name__)
  
  @app.route('/datetime')
  def get_datetime():
      """ Create a web API with Python and Flask to give the current date and time.
      >>> from flask import Flask
      >>> import datetime
      >>> app = Flask(__name__)
      >>> @app.route('/datetime')
      ... def get_datetime():
      ...     return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
      >>> app.test_client().get('/datetime').data.decode('utf-8')
      '2021-10-10 12:34:56'  # Replace with the actual current date and time
      """
      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")
  
  if __name__ == '__main__':
      app.run()