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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 add(self, lineitem):
 """ Add a line item record to this Costs object. """

        # Check for a ProductName in the lineitem.
        # If its not there, it is a subtotal line and including it
        # will throw the total cost calculation off.  So ignore it.
        if lineitem['ProductName']:
            self._lineitems.append(lineitem)
            if lineitem['BlendedCost']:
                self._blended_cost += lineitem['BlendedCost']
            if lineitem['UnBlendedCost']:
                self._unblended_cost += lineitem['UnBlendedCost']