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Overriding UserList methods

Steve Holden sholden at holdenweb.com
Mon Mar 5 00:52:40 EST 2001 
"Daniel Klein" <danielk at aracnet.com> wrote in message
news:b566atck0ruu4tae8n1srrkntbmme26gor at 4ax.com...
> I must be missing something, cos I can't figure out how to override a
method
> using the UserList module. Here is some code:
>
> import UserList
> class MyList(UserList.UserList):
>       __def __init__(self):
>         UserList.UserList.__init__(self)
>
While this would work, I don't see it's strictly necessary. Why not just
inherit the __init__ method from UserList?

>     def append(self, object):
>         self.append(object)
>
> Understandably, this goes into a recursive frenzy until it hits the stack
> limit. :-(
>
Well, if you want *you* append method to make use of UserList's method you
would have to write

    def append(self, object):
        UserList.append(self, object)

Since all you are doing is reflecting the underlying UserList's append()
method, however, it would seem to make more sense to simply allow append()
to be inherited as well!

> The only way I could get this to work was to give the method another name,
ie
>
>     def add(self,object):   ## This works but I would rather use 'append'
>         self.append(object)   ## as the method name.
>
> So how can I override the append() method so that I can add my specialized
code
> to it?
>
> Daniel Klein

The clue is to use the unbound method from the superclass, as I showed you
above.

Another way would be to create a UserList object as an instance variable,
and then delegate methods to the UserList which you don't recognize, but
this might be going too far.  Hope this helps.

regards
 Steve
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