[Tutor] custom container subclassing list-- slices are lists!?

[Marcus Goldfish]

On 8/21/06, Marcus Goldfish <magoldfish at gmail.com> wrote:

> I'd like to sublcass the built-in list type to create my own container.
> How can I make slices of the list be of type myclass-- currently they are
> lists.  Example:
>
> >>> class MyFoo(list):
>            def __init__(self, inlist):
>                   self = inlist[:]
> >>> me = MyFoo(range(10))
> >>> type(me)
> <class '__main__.MyFoo'>
>
> >>> type(me[0:3])
> <type 'list'>
>

First, a better example class:

class MyFoo(list):
   def __init__(self, inlist):
      list.__init__(self, inlist)

Second, I think I found a partial answer in the Feb 22, 2005 tutor thread
http://aspn.activestate.com/ASPN/Mail/Message/python-tutor/2502290.  To
preserve type, I need to override some special functions.  In the case of
slicing, I need to override with something like this:

def __getslice__(self, i, j):
   return MyFoo(list.__getslice__(self, i, j))

This seems straightforward, but raises other questions: what other functions
should I override, e.g., __add__, __radd__?  Is there a preferred pythonic
way to creating a custom list container?

Finally, should I slice-copy my input list, inlist, to prevent side effects,
or is this handled by list?

Thanks,
Marcus
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