[Tutor] Need Explanation...

[Max gmail]

On Dec 10, 2011, at 12:04 PM, Alan Gauld wrote:

> On 10/12/11 16:46, Steven D'Aprano wrote:
> 
>> ...the alternative would also have caught out everybody at some point.
>> Consider a hypothetical Python where mutator methods returned a result:
>> 
>> a = [1, 2, 3]
>> b = a.append(4)
>> 
>> Does this mean...?
>> 
>> * append 4 to a, then return a (and therefore a and b are
>> alternative names for the same list)
> 
> This is what I'd expect.
> I'm thinking about the Smalltalk model where  the default return
> value from a method is self...
> 
> I'm particularly sensitive to this just now because I'm playing
> with Squeak (again) and the elegance and consistency of
> Smalltalk's mechanism  stands in stark contrast to the mixed
> model in Python. (OTOH Smalltalk overall is a frustrating
> experience for me, I would like to love it but never quite
> get there... :-)

Personally, I found that returning a copy of a seemed more logical- after all, if you return 4 to b, then adding 2 to b wouldn't make 4 equal 6.
> 
>> circumstances, regardless of which behaviour was choosen for append, it
>> would catch out some people some time.
> 
> Probably, although if returning 'self' were the default (which
> of course only makes sense in a pure OO world like Smalltalk) people would get used to the semantics. Consistency is all in these kinds of situations. Sadly its one of the few areas where Python is slightly inconsistent.
> 
>> A better alternative would be for Python to have procedures as well as
>> functions/methods, so that:
>> 
>> b = a.append(4)
>> 
>> would raise an exception immediately.
> 
> Better than silently returning None for sure.

Of course, by silently returning None, you can just go on with your daily life and be happily ignorant of any return value; in other more strongly typed languages, the void functions/methods tend to alter other variables and situations more than, for example, ints.  I feel myself that it is no more trouble to simply type 'a.append(4); b = a'.
> 
> -- 
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> 
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