Register to streaming market data updates
        https://www.interactivebrokers.com/en/software/api/apiguide/java/reqmktdepth.htm

def requestMarketDepth(self, contracts=None, num_rows=10):
        """
        Register to streaming market data updates
        https://www.interactivebrokers.com/en/software/api/apiguide/java/reqmktdepth.htm
        """

        if num_rows > 10:
            num_rows = 10

        if contracts == None:
            contracts = list(self.contracts.values())
        elif not isinstance(contracts, list):
            contracts = [contracts]

        for contract in contracts:
            tickerId = self.tickerId(self.contractString(contract))
            self.ibConn.reqMktDepth(
                tickerId, contract, num_rows)