def shellComparator(shell, vehicle):
    if vehicle is not None:
        vDescriptor = vehicle.descriptor
        basicShellDescr = getBasicShell(vDescriptor)
        return ItemsComparator(params.ShellParams(shell.descriptor, vDescriptor).getParamsDict(), params.ShellParams(basicShellDescr, vDescriptor).getParamsDict())
    else:
        return
 def isBasic(self):
     return self._vehicleDescr is not None and getBasicShell(self._vehicleDescr).compactDescr == self._itemDescr.compactDescr