[Tutor] Differnce between java and python

[Alan Gauld]

>>Another example is that Python supports "Duck Typing", that is
>>its type checking  is protocol based.
>
> I see your point, but duck typing seems awfully implicit and
> behind-the-scenes.

When you first encounter it it is. I came from a C++ and Pascal
background where strict typing was the rule, Python seemed very lax.
But I had the advantage of having worked in Lisp and Smalltalk too
so I kind of relaxed fairly quickly.

> Seems like if I expect a protocol, and you provide something that claims 
> to
> implement said protocol, there ought to be some contract that ensures 
> we're
> dealing with the same protocol. I ought not to be able to pass my car and
> my nose to the same function, just because the both run().

It depends. Obviously in this example its likely that the behaviour would
result in boizarre results but on the other hand if the function was
race(obj1, obj2) then both car and nose could be appropriate,
but in the latter case with rather horrible connotations...

But seriously, Duck Typing allows for a far more expreessive and
powerful use of objects. When you are no longer bound by the limitations
of inheritance heirarchies you can start to build much more powerful 
funcions.
The downside is that there is an onus on the client to sanity check the
usage of the function - will it really do what I expect?

Alan G
Author of the learn to program web tutor
http://www.freenetpages.co.uk/hp/alan.gauld