differentially loading a class at runtime

[Maurice LING]

Hi,

In normal circumstances, we know exactly which class to load and use 
using compile time. But I am now faced with a situation whereby I need 
to load a class differentially at runtime (the user can define which 
class to load).

For example:

class a:
	......

class b:
	......

allowed = ['a', 'b']

'allowed' list will store the names of the alternative classes to use. 
The alternative classes have the same set of methods but different 
implementations.

How can I differentially use the classes at runtime?

Thanks
Maurice