How do you control _all_ items added to a list?

[Xif]

Hi

I want to have control over all items added to a list.

The first attempt was to subclass list and override its .append()
method.

Problem is, there are plenty of other ways the list can have items
added to it - e.g. extend, insert - and theyr'e not at all affected by
the changes I made to append.

Is there some "base" item-adding method that all other item-adding
methods use, so I can override it and have the changes affect all
item-adding functions?

Thanks,
Xif

 

[Fuzzyman]

Hi

I want to have control over all items added to a list.

The first attempt was to subclass list and override its .append()
method.

Problem is, there are plenty of other ways the list can have items
added to it - e.g. extend, insert - and theyr'e not at all affected by
the changes I made to append.

Is there some "base" item-adding method that all other item-adding
methods use, so I can override it and have the changes affect all
item-adding functions?

If you subclass list then you will need to override all methods that
can set items. This is because the built in methods work directly with
the internal structure and are implemented in C. It's a bit of a
pain... but not that much.

Regards,

Fuzzy
http://www.voidspace.org.uk/python/index.shtml

 

[Xif]

Quoting Fuzzyman:

"If you subclass list then you will need to override all methods that
can set items."


Overiding all those methods is too much of an effort. I don't really
need them.

I'll just have an object that uses a list internally, and define only
the two methods I really need: extend() and getItems().

That way I retain full control over what goes into the private
obj._list, without the superfluous work of overriding all those methods
I don't really need.

Thanks for your help,
Xif

 

[Nick Coghlan]

Overiding all those methods is too much of an effort. I don't really
need them.

Hmm, it might be nice if there was a UserList.ListMixin that was the counterpart
to UserDict.DictMixin that let's you provide the full dictionary API with just
__getitem__, __setitem__, __delitem__ and keys()

With an appropriate ListMixin, providing the first three methods would suffice
to support the full list API.

Cheers,
Nick.