input: from Crypto.Cipher import AES
  
  def encrypt_decrypt_string(action, text):
      """Encrypt or decrypt a string using AES encryption.
      The function takes an action ("encrypt" or "decrypt") and a text string.
      It uses a pre-defined key for AES encryption in ECB mode.
      The function returns the encrypted or decrypted text.
      
      >>> encrypt_decrypt_string("encrypt", b'Hello, World!')
      b'Y\x83~\xe9\xcb7Wf4\xfb\x93\xae\xb4)\x95\xde'
      >>> encrypt_decrypt_string("decrypt", b'Y\x83~\xe9\xcb7Wf4\xfb\x93\xae\xb4)\x95\xde')
      b'Hello, World!'
      """
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      
      if action == "encrypt":
          return cipher.encrypt(text)
      elif action == "decrypt":
          return cipher.decrypt(text)
      else:
          return "Invalid action"
output:     key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      
      if action == "encrypt":
          return cipher.encrypt(text)
      elif action == "decrypt":
          return cipher.decrypt(text)
      else:
          return "Invalid action"