Withholds offers/bids with invalid (<= 0.0) quantities or prices
            outwith the set limits.

def _withholdOffbids(self):
        """ Withholds offers/bids with invalid (<= 0.0) quantities or prices
            outwith the set limits.
        """
        limits = self.limits

        # Eliminate offers (but not bids) above 'price_cap'.
        if not limits.has_key('max_offer'):
            limits['max_offer'] = self.priceCap

        # Limit cleared offer prices after locational adjustments.
        if not self.limits.has_key('maxClearedOffer'):
            self.limits['maxClearedOffer'] = self.priceCap

        # Withhold invalid offers/bids.
        for offer in self.offers:
            if round(offer.quantity, 4) <= 0.0:
                logger.info("Withholding non-posistive quantity [%.2f] "
                            "offer." % offer.quantity)
                offer.withheld = True

        for bid in self.bids:
            if round(bid.quantity, 4) <= 0.0:
                logger.info("Withholding non-posistive quantity [%.2f] "
                            "bid." % bid.quantity)
                bid.withheld = True

        # Optionally, withhold offers/bids beyond price limits.
        if limits.has_key("maxOffer"):
            for offer in self.offers:
                if offer.price > limits["maxOffer"]:
                    logger.info("Offer price [%.2f] above limit [%.3f], "
                        "withholding." % (offer.price, limits["maxOffer"]))
                    offer.withheld = True

        if limits.has_key("minBid"):
            for bid in self.bids:
                if bid.price < limits["minBid"]:
                    logger.info("Bid price [%.2f] below limit [%.2f], "
                        "withholding." % (bid.price, limits["minBid"]))
                    bid.withheld = True