input: Write a function to encrypt a message using a key in Python by adding the ASCII value of each character of the message with the ASCII value of the first character of the key. Return the encrypted message.
  assert encrypt("Hello world!", "secret")=="Djjn]wjrvn&"
  assert encrypt("Python programming", "code")=="Tk|uz`wvutrtvgx"
  assert encrypt("", "key")==""
  assert encrypt("Testing encryption", "test")=="Yjxynsljyiq}tsk"
  assert encrypt("Secure coding", "password")=="Wh{vnkspxty"
output: def encrypt(message, key):
      encrypted_message = ""
      key_char = ord(key[0])
      for char in message:
          encrypted_message += chr(ord(char) + key_char)
      return encrypted_message