larry-discuss team mailing list archive

[Keith Goodman <kwgoodman@xxxxxxxxx>]

On Sun, Feb 7, 2010 at 5:26 PM, Keith Goodman <kwgoodman@xxxxxxxxx> wrote:
> On Sat, Feb 6, 2010 at 6:53 PM,  <josef.pktd@xxxxxxxxx> wrote:
>> On Sat, Feb 6, 2010 at 9:48 PM, Keith Goodman <kwgoodman@xxxxxxxxx> wrote:
>>> On Sat, Feb 6, 2010 at 5:38 PM, Keith Goodman <kwgoodman@xxxxxxxxx> wrote:
>>>> In a blueprint titled "index-by-label" I proposed a way to index
>>>> larrys by lists of label elements. Here's a simpler, but less
>>>> versatile, proposal. On the whole, due to its simplicity, I think it
>>>> is more powerful.
>>>
>>> I commit this proposal in r187. Please give it a try.
>>
>> I will try it tomorrow and look at the implementation.
>> My first reaction: very convenient but potentially fragile for arbitrary labels.
>
> The rule is simple for indexing with a string S:
>
> 1. Look for string S in the label. If found you are done. If not found...
> 2. Map the labels to strings and look again
>
> Although the rule is simple, the result can be unexpected in corner
> cases. For example, you may try to index with str(1) to access the
> label integer 1 but the label could also contain string '1'. So in
> that case you'd get an unexpected result even though the rule is
> simple.
>
> I could add a check: len(set(strlabel)) == len(set(label)). And raise
> an IndexError (or is that ValueError?) if they are not equal. That
> will slow things down but only for indexing by strings.
>
> Would that address your fragile comment? Or do you have something else in mind?

Wait, that's being too restrictive. We don't care if there are
duplicates in strlabel. We only care if S appears more than once in
strlabel. For example, if we are indexing with str(1) and the label is
[2, str(2), 1], then we don't care that strlabel = [str(2), str(2),
str(1)] has duplicates; we only care that str(1) only appears once. If
we were indexing with str(2), on the other hand, then there would be a
problem and we'd raise a ValueError.

I can add that check and then you can take a look.