[Tutor] Changing a class into a subclass

[Kent Johnson]

Max Noel wrote:
> 
> On Mar 24, 2005, at 18:07, Ismael Garrido wrote:
> 
>> Hello.
>>
>> I have a program that saves/loads to/from XML. I have a main class 
>> Building, and a subclass House(Building). When I save the code I 
>> instruct each object to save itself to XML (using ElementTree), so 
>> House adds itself to the XML tree.
>> My problem is when I load the XML. Before having subclasses what I did 
>> was to send the XML object (again in ElementTree) to the object and 
>> let itself load. Now, with subclasses, if I send the House XML to 
>> Building I get a Building instance, when I need a House instance.
> 
> 
>     You can't make an object transform into an object of a different 
> class. 

Amazingly enough, you actually can do this just by rebinding self.__class__! This thread has an example:
http://groups-beta.google.com/group/comp.lang.python/browse_thread/thread/15afbbcd502b5450/fa111e6ea9ee4cc4

You need to identify what class the object will be an instance of
> before loading it. Which, if you're using XML tags like <Building 
> type="House"> or <House>, shouldn't be very difficult to do.

This is a better approach than changing __class__ after the fact.

Kent