input: Write a function to encrypt and decrypt strings using a chosen cipher text algorithm in Python. The application should take a string as input for encryption or decryption, and return the corresponding encrypted or decrypted string using the AES algorithm in ECB mode.
  
  from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt(plaintext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext)
  
  def decrypt(ciphertext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)
  
  assert encrypt("Hello World!".encode()) == b'\xe5E\x7f\xdfD\xd6V\xf87\x18xeQ)\xcb'
  assert decrypt(b'\xe5E\x7f\xdfD\xd6V\xf87\x18xeQ)\xcb') == b'Hello World!'
output: def encrypt(plaintext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext)
  
  def decrypt(ciphertext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)