code: def aes_pad_key(key):
      
      if len(key) in (16, 24, 32):
          return key
      if len(key) < 16:
          return pad(key, 16, zero=True)
      elif len(key) < 24:
          return pad(key, 24, zero=True)
      else:
          return pad(key[:32], 32, zero=True)
docs: AES keys must be either 16, 24, or 32 bytes long. If a key is provided that is not
      one of these lengths, pad it with zeroes (this is what pgcrypto does).