Derived class and deepcopy

[Philip Smith]

Hi

If I derive a class (eg Matrix) from list I presume this implies the classic 
OOP 'is a' relation between the derived and super class.

I therefore presume I can use a derived class in any context that I can use 
the superclass.

In the given example I want to apply deepcopy() to the Matrix instance (on 
initialisation) to ensure that the list part is not affected by subsequent 
changes to the initialising list or Matrix but this gives me a string of 
errors (some of which imply I'm trying to copy the class rather than the 
instance).

Anyone got any thoughts on this????

Phil