code: def web3_sha3(self, data):
          
          data = add_0x(binascii.hexlify(str(data).encode('utf-8')))
          return (yield from self.rpc_call('web3_sha3', [data]))
docs: https://github.com/ethereum/wiki/wiki/JSON-RPC#web3_sha3
  
          :param data: Data for hashing
          :type data: str
  
          :return: Keccak-256
          :rtype: str