https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_getbalance

        :param address: Account address
        :type address: str

        :param block: Block tag or number (optional)
        :type block: int or BLOCK_TAGS

        :return: wei
        :rtype: int

def eth_getBalance(self, address, block=BLOCK_TAG_LATEST):
        """https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_getbalance

        :param address: Account address
        :type address: str

        :param block: Block tag or number (optional)
        :type block: int or BLOCK_TAGS

        :return: wei
        :rtype: int
        """
        block = validate_block(block)
        return hex_to_dec((yield from self.rpc_call('eth_getBalance',
                                                    [address, block])))