models.py

    def save(self, **kwargs):
        self.flag_cached_attrs_as_stale()
        self.react_to_purchasing_status()
        if not self.id:
            self.payment_term = self.vendor.payment_term
            if self.freight_method in (FREIGHT_CC_FULL, FREIGHT_CC_LTL):
                self.common_carrier_pickup_address = self.vendor.any_warehouse_contact
        if self.common_carrier_pickup_address:
            if(not self.common_carrier_pickup_address.the_same_address_as(self.historic_common_carrier_pickup_address)
               and self.phase <= PHASE_RECEIVING):
                ccpa = CommonCarrierPickupAddress()
                ccpa.copy_address_from(self.common_carrier_pickup_address)
                ccpa.save()
                self.historic_common_carrier_pickup_address = ccpa
        if self.vendor.vendorcontact_set.filter(contact_type='main').exists():
            self.vendor_contact = self.vendor.vendorcontact_set.filter(contact_type='main')[0]
        if self.vendor.vendorcontact_set.filter(contact_type='broker').exists():
            self.broker_to_copy = self.vendor.vendorcontact_set.filter(contact_type='broker')[0]

        super(Purchase, self).save(**kwargs)

        self.update_lines_for_status()

This is from /apps/purchasing/models.py in the Purchase class

By the time we get to self.update_lines_for_status() we have purchase lines, but I don't see where they are created?