Customizing sequence types

[Chris Rebert]

On Sun, Nov 16, 2008 at 8:16 AM, Mr. SpOOn <mr.spoon21 at gmail.com> wrote:
> Hi,
> I'm trying to create a class which inherit a list to change some behavior.
> This list should contain other instance objects and has to manage
> these instances in a particular way.
>
> 1) I need to sort this elements in this list, but they must be sorted
> using an instance variable. What does Python use to sort elements? I
> mean, there is a __sort__ method in the class list or it just uses
> comparison operators? In this case, shall I just redefine this
> operators in the element classes?

It uses the comparison operators. IIRC, at a minimum it needs __lt__
and __eq__ to be defined on the elements.

>
> 2) I need to have just unique elements. Maybe this is related to first
> question (or maybe not). Again, to estabilish the uniqueness of an
> element I have to use an instance variable. I think I have to rewrite
> both the methods append() and __contains__(), but I'm not sure how.
>
> For the first one I did:
>
>    def append(self, element):
>        if element in self:
>            pass
>        else:
>            list.append(self, element)

You should probably use the `bisect` module
(http://docs.python.org/library/bisect.html) for searching and
inserting into the list as it takes advantage of and ensures that the
list keeps sorted. It also means that __contains__ and some other
operations become O(log N) rather than O(N).

Cheers,
Chris
-- 
Follow the path of the Iguana...
http://rebertia.com

>
> It seems right to me, but I have no idea what to do with __contains__()
>
> Suggestion?
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