Why no list heritable type?

[Jeff Shannon]

Sion Arrowsmith wrote:

>In article <86vfb13jpl.fsf at guru.mired.org>, Mike Meyer  <mwm at mired.org> wrote:
>  
>
>>And before Python 2.2 there was the UserList class in the standard
>>library. Which is still there in 2.4. Shouldn't it be depreciated by
>>this point?
>>    
>>
>
>Apart from compatibility issues as mentioned in the UserList
>documentation, deriving from it will give you a classic class,
>whereas deriving from list will give you a new style class.
>There may be circumstances under which this is important
>(exercise left to more twisted minds than mine). Same applies
>to dict/UserDict.
>  
>

Additionally, as I understand it UserList and UserDict are implemented 
entirely in Python, which means that there can be significant 
performance differences as well.  There's very little benefit to 
UserList/UserDict now that builtins can be subclassed, and I believe 
that they are still there only as a matter of backward compatibility.

Jeff Shannon
Technician/Programmer
Credit International