Useful built-in functions

You have used built-in functions, such as send, assert, as_wei_value, concat, and convert. However, there are other useful functions, such as the following:

first_name: bytes[10] = slice(name, start=0, len=10)
length_of_name: int128 = len(name)
selfdestruct(self.donatee)
round_heart: int128 = ceil(half_of_my_heart)
round_heart: int128 = floor(half_of_my_heart)
secret_hash: bytes32 = sha3('messi')