def get_block_sys_fee(self, block_index, **kwargs):
return self._call(JSONRPCMethods.GET_BLOCK_SYS_FEE.value, [block_index, ], **kwargs)<EOL>
Returns the system fees associated with a specific block index.

        :param block_index: a block index (block height)
        :type block_index: int
        :return: system fees of the block, expressed in NeoGas units
        :rtype: str