input: from typing import List
  
  def encrypt(message: str, key: str) -> str:
      """ Encrypt a given message using a key. Each character in the message
      is shifted by the ASCII value of the first character of the key.
      >>> encrypt("Hello world!", "secret")
      'Ts}$)$'τʃϒτ−
      """
output:     encrypted_message = []
      shift = ord(key[0])
      for char in message:
          encrypted_message.append(chr(ord(char) + shift))
      return ''.join(encrypted_message)