obj *and* obj['foo']
jonathan at onegoodidea.com
Wed Aug 7 03:45:19 EDT 2002
On 6/8/2002 23:11, in article ul0ich5k1nu27 at corp.supernews.com, "Travis
Shirk" <travis at pobox.com> wrote:
> I'm trying to write a class that implements __getitem__(self, k),
> but I'd like to invoke the method with integer keys and string keys.
> Currently, I'm getting exceptions when I use string keys:
> TypeError: sequence index must be integer
> I'm subclassing list (python 2.2) so I understand why the *sequence* does
> not allow non-int keys, and I assume that if I subclassed dict the reverse
> type clash would occur.
> So, is there a way to "override" __getitem__ to accept both types of
Do you really need to subclass 'list'? i.e., do your things have to satisfy
the condition 'isinstance(mything, list)'? If not, don't subclass list and
you'll have no problems. The normal '__getitem__' function can take any
The problem with subclassing list is that you end up in the dark world of
Python C-type prototols where sequences and mappings are different things.
The type subclassing magic fakes up what looks like a standard __getitem__
call, except by that point it's too late and you've been forced through the
sequence protocol and the argument must be an integer.
Just write a class like so:
>>> class Foo:
... def __getitem__( self, item ):
... print 'Item was:', item
... return 5
>>> f = Foo()
Item was: 7
Item was: hello
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