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