[Python-ideas] List Revolution

[Massimo DiPierro]

I was about to propose this:

class List(list):
    def __getitem__(self,i):
        """                                                                                           
        a = List()                                                                                    
        a.append(4)                                                                                   
        a.appned(5)                                                                                   
        print a[0.5]                                                                                  
        4.5                                                                                           
        """
        if isinstance(i,(int,long)): return list.__getitem__(self,i)
        else:
            j = int(i)
            x = i - j
            return self[j]*(1.0-x)+self[j+1]*x


On Sep 10, 2011, at 8:51 PM, Nick Coghlan wrote:

> On Sun, Sep 11, 2011 at 10:37 AM, Steven D'Aprano <steve at pearwood.info> wrote:
>> 0-based indexes are useful for some tasks, and less useful for other tasks.
>> In my experience, I find that 0-based indexing is more useful most of the
>> time: it leads to fewer off-by-one errors.
>> 
>> 1-based indexes are particularly well-suited for programming languages using
>> a natural language metaphor, usually aimed at non-programmers. Examples
>> include Xion, Applescript, and Inform-7.
> 
> Indeed, the concepts of half-open ranges and 0-based indexing go hand
> in hand (as described in the EWD article), and it ties directly in to
> the notion of *index arithmetic*.
> 
> A case that illustrates this nicely is that of partitioning a
> sequence. Suppose we want the first 5 items in one subsequence and the
> rest in another. This is easy to write, and requires no adjustments to
> the numbers:
> 
>  head = seq[:5]
>  assert len(head) == 5
>  tail = seq[5:]
>  assert len(tail) == len(seq) - 5
> 
> Zero based indexing (in conjunction with half-open ranges) makes the
> arithmetic work out nicely, and, in practice, that turns out to be
> important when it comes to writing correct programs.
> 
> However, it comes at the cost of breaking the intuitive mapping to the
> counting numbers: the first item is at offset 0, the second is at
> offset 1, etc. This is a definite downside, but the collective
> judgment of many language designers is that the reduction in
> off-by-one errors when manipulating indices is worth the additional
> difficulty in learning the language for programming novices.
> 
> Cheers,
> Nick.
> 
> -- 
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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