a clean way to define dictionary

Chermside, Michael mchermside at ingdirect.com
Thu Jun 19 19:06:40 CEST 2003


Skip Montanaro wrote:

> 
>     >> In 2.3, you can express this as dict(foo=1, bar='sean') without a
>     >> need to define a function for the purpose.
> 
>     Alexander> Yuck! This seems like a really bad idea to me. This
>     Alexander> effectively makes it impossible to specify any options
>     (such Alexander> as initial size, default value etc.)
> 
> I don't see that the behavior of dict() affects your ability to define the
> behavior of a subclass.

Alex Martelli replies:
> To play devil's advocate -- it does so by Liskov substitution principle
> (if all keywords must be passed untouched to built-in dict to emulate
> its behavior, you can't steal some of them to control your subclass's,
> within the constraint of being able to drop your subclass in lieu of
> dict into an existing piece of code without breaking it).

Please help me understand this. I thought LSP said essentially that
INSTANCES of the subclass should be drop-in replacements for INSTANCES
of the superclass. But the constructor is really not a property of
INSTANCES... it's clearly a property of the class itself. So... am I
missing something here?

-- Michael Chermside

PS: I do agree that it's mildly annoying for subclassing dict, and that
it's mildly useful for brevity & clarity in declaring some dicts, and
that if anyone actually OBJECTS (which I don't) that python-dev is the
place to speak up pretty-darn-quick.

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