input: 
  def encrypt_decrypt(mode: str, text: str) -> str:
      """Encrypts or decrypts a given string using AES encryption.
      The function supports two modes: 'encrypt' and 'decrypt'.
      It uses a fixed key for encryption and decryption.
      
      >>> encrypt_decrypt('encrypt', 'Hello World!')
      'n$¨Ç7ßIhttps://www.python.org/_NuW‡7ßET``Ör†ötN¡;'
      >>> encrypt_decrypt('decrypt', 'n$¨Ç7ßIhttps://www.python.org/_NuW‡7ßET``Ör†ötN¡;')
      'Hello World!'
      """
      key = b'Sixteen byte key'
      if mode == 'encrypt':
          cipher = AES.new(key, AES.MODE_ECB)
          return cipher.encrypt(text)
      elif mode == 'decrypt':
          cipher = AES.new(key, AES.MODE_ECB)
          return cipher.decrypt(text)
      else:
          return "Invalid mode"
  
output:     
      from Crypto.Cipher import AES
      import base64
  
      def pad(s):
          return s + (AES.block_size - len(s) % AES.block_size) * chr(AES.block_size - len(s) % AES.block_size)
  
      def unpad(s):
          return s[:-ord(s[len(s)-1:])]
  
      if mode == 'encrypt':
          text = pad(text)
          cipher = AES.new(key, AES.MODE_ECB)
          encrypted_text = cipher.encrypt(text.encode('utf-8'))
          return base64.b64encode(encrypted_text).decode('utf-8')
      elif mode == 'decrypt':
          encrypted_text = base64.b64decode(text)
          cipher = AES.new(key, AES.MODE_ECB)
          decrypted_text = cipher.decrypt(encrypted_text)
          return unpad(decrypted_text.decode('utf-8'))
      else:
          return "Invalid mode"
  