code: def get_checking_block(self):
          
          checking_block = 'pending'
          if self.eth_node is constants.EthClient.PARITY:
              checking_block = 'latest'
          return checking_block
docs: Workaround for parity https://github.com/paritytech/parity-ethereum/issues/9707
          In parity doing any call() with the 'pending' block no longer falls back
          to the latest if no pending block is found but throws a mistaken error.
          Until that bug is fixed we need to enforce special behaviour for parity
          and use the latest block for checking.