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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def startTicker(self, reqId, contract, tickType):
 """ Start a tick request that has the reqId associated with the contract. Return the ticker. """

        ticker = self.tickers.get(id(contract))
        if not ticker:
            ticker = Ticker(
                contract=contract, ticks=[], tickByTicks=[],
                domBids=[], domAsks=[], domTicks=[])
            self.tickers[id(contract)] = ticker
        self.reqId2Ticker[reqId] = ticker
        self._reqId2Contract[reqId] = contract
        self.ticker2ReqId[tickType][ticker] = reqId
        return ticker