docs: 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])))