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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 createComboContract(self, symbol, legs, currency="USD", exchange=None):
 """ Used for ComboLegs. Expecting list of legs """

        exchange = legs[0].m_exchange if exchange is None else exchange
        contract_tuple = (symbol, "BAG", exchange, currency, "", 0.0, "")
        contract = self.createContract(contract_tuple, comboLegs=legs)
        return contract