Python supports LSP, does it?

Jules Dubois mknhln002 at sneakemail.com
Wed Aug 10 04:35:23 CEST 2005


On Tuesday 09 August 2005 17:36, Andy Leszczynski
<leszczynscyATnospam.yahoo.com.nospam> <>
(<hJSdnSuJuKa5oWTfRVn-gw at comcast.com>) wrote:

> wikipedia
>
(http://en.wikipedia.org/wiki/Python_programming_language#Object-oriented_programming)
> says:
> """
> Python's support for object oriented programming paradigm is vast. It
> supports polymorphism [...] fully in the Liskov substitution
> principle-sense for all objects.
> """
> 
> Just wondering if it is true statement.

It's true if not particularly insightful.

    "What is wanted here is something like the following substitution
    property [6]: If for each object o1 of type S there is an object
    o2 of type T such that for all programs P defined in terms of T,
    the behavior of P is unchanged when o1 is substituted for o2, then
    S is a subtype of T."

> Is not LSP more a quality of the desing of class hierachy rather then
> language itslef? 

In a statically-typed language, polymorphism is based on the class hierarchy
(through inheritance).  Because Python uses dynamically-checked typing, its
polymorphism is structural rather than nominative.

> Comments?

Discussions like these might be more appropriate for the comp.object
newsgroup.



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