[Tutor] Changing a class into a subclass

Kent Johnson kent37 at tds.net
Thu Mar 24 19:55:14 CET 2005

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:

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.


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