input: from flask import Flask
  import datetime
  
  
  def web_api_datetime():
      """ Create a web API with Python and Flask to give the current date and time.
      >>> app = Flask(__name__)
      >>> @app.route('/datetime')
      ... def get_datetime():
      ...     return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
      >>> if __name__ == '__main__':
      ...     app.run()
      The above code will create an API endpoint '/datetime' that returns the current date and time in the format 'YYYY-MM-DD HH:MM:SS'.
      """
output:     app = Flask(__name__)
      
      @app.route('/datetime')
      def get_datetime():
          return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
      
      if __name__ == '__main__':
          app.run()